Mollusca: India

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Faunal Diversity in India: Mollusca

This is an extract from FAUNAL DIVERSITY IN INDIA Edited by J. R. B. Alfred A. K. Das A. K. Sanyal. ENVIS Centre, Zoological Survey of India, Calcutta. 1998 ( J. R. B. Alfred was Director, Zoological Survey of India)

Introduction

Molluscs are soft-bodied animals, a majority of which are covered by a hard calcareous shell. The shell may consist of one, two or many pieces or sometimes it may be internal and cartilaginous. The phylum includes a heterogeneous group of organisms, which are popularly known as 'shells' or by different names such as snails, slugs, mussels, oysters, clams, cuttle fishes, squids, octopuses, etc. The story of molluscan success in the history of evolution is evident from their long and rich fossil records. By the time the molluscs appeared in the Cambrian, they were already differentiated into different classes. The phylum is divided into seven classes, of which five are represented in India. The shells, which are the 'abandoned houses' of molluscs are popular objects of collection for hobbyists and amateur curio collectors. The shells which are beautiful architectural structures with an aesthetic appeal, have fascinated man from prehistoric times, as evidenced by their remains in Mohenjodaro, Harappa and other places. The socio-economic importance of molluscs is reflected in their use.in folklore, in currency, valuable ornaments, in their edible value, etc. Molluscs have successfully colonised almost all ecosystems and habitats.

Status Of The Taxon

Global and Indian Status

Global estimates of molluscan diversity vary between 50,000 and 1,50,000 species. A conservative estimate as reflected in Table 1 includes 66,535 species for the world. Molluscan diversity in India is 7.62 per cent of the total global diversity which is in fact higher than that of the total faunal percentage of India i.e. 6.67. The diversity is contributed mainly by marine molluscs, whose knowledge is far from complete. Hitherto, the work in India has been mainly concentrated on common and easily available malacofauna, which do not involve any special techniques of sampling. It is expected that actual diversity may be more than the present estimates.

Distribution

Molluscs have adapted themselves to diverse habitats, from the deep sea (3000 m) of Andamans to higher elevations (about 5000 m) in the Himalayas. But the diversity and abundance is more in the rocky intertidal zone along the coast and in the coral reef ecosystem of Gulf of Mannar, Gulf of Kutch, Lakshadweep and the Andaman & Nicobar Islands. Sandy coasts support less, but typical interstitial fauna.

From the available data it is possible to identify certain areas having rich molluscan diversity. Andaman and Nicobar Islands have a rich molluscan diversity, which include about 1150 species distributed in marine (1000 spp.), land (110 spp.) and freshwater (40 spp.) ecosystems. Gulf of Mannar, including the Coromandel coast, and Lakshadweep have 428 and 424 species, respectively. Gulf of Kutch (Gujarat coast) and Orissa coast account for 350 and 337 species, respectively. The diversity in these areas is mainly due to preponderance of marine molluscs. As far as land molluscs are concerned diversity is concentrated in North eastern India and Western Ghats. From Meghalaya alone, which has been sampled recently, a total of 223 species of land and freshwater molluscs have been reported.

Biological Diversity And Its Special Features

Molluscan Diversity

The phylum Mollusca is distinguished into three subphyla, namely Aculifera, Placophora and Conchifera. The first mentioned includes only one class, Aplacophora, which however, does not occur in Indian Seas. The subphylum Placophora also includes one class known as Polyplacophora, the representatives of which are popularly called chitons. It is a small class with an estimated number of 500 species. The subphylum Conchifera is divided into five classes, namely Monoplacophora, Gastropoda, Bivalvia, Scaphopoda and Cephalopoda. The first mentioned does not occur in Indian seas. Thus out of seven recognized classes of the phylum Mollusca, five classes mentioned, have their representatives in India. Taxonomy of many families of molluscs is still in a confused state. It is difficult to mention precisely the number of families within the phylum. Against general estimated total of 586 families in the phylum, about 290 families presumably occur in the Indian subcontinent and its territorial waters. There are only a few number of taxonomists who have undertaken studies on Indian molluscs and as a result, knowledge on Indian molluscs is far from complete. From the existing knowledge, the following is the break up of families as far as India is concerned. Table• 2 Number of families from India Class Families (n)

At the family level, about 62.8 per cent of the families known from the world are represented in India. The occurrence of diverse ecosystems and habitats in India has given scope for rich species diversity. The estimates have been made on the basis of available literature and field observations. The data on land and freshwater molluscs can be taken as a true representation of the position. But these estimates are based largely on the old data. The modem biological species concept and revisionary studies may bring down the number of species. A recent revision of a freshwater family-Lymanaeidae has brought down the number of species from 1000 to 40.

A comparison with the world malacofauna shown in Table 1 reveals that Cephalopods (Cuttle fishes, squids, octopuses, nautilus etc.) represent 35.00 per cent of the total species diversity. These are highly mobile with extensive ranges and support valuable fisheries for the country. The other classes include molluscs which are less mobile and have narrow ecological requirements.

The diversity of molluscs varies with the ecosystem. An analysis has been attempted earlier (Subba Rao, 1991) and the same is presented below, with an up date where necessary. Table -3 Molluscan Diversity in Terrestrial and Wetland (Freshwater) ecosystems Class/Subclass Families(n) Genera (n) Species Terres-Fresh Terres-Fresh Terres-Fresh trial water trial water trial water Gastropoda Prosobranchia 5 11 32 26 536 66 Pulmonata 21 3 108 8 951 36 Bivalvia 8 19 81 Total 26 22 140 53 1487 183

Table• 4 Estimated molluscan diversity in marine ecosystem

From the tables 2 and 3, it can be seen that diversity at all levels is more in the marine ecosystem followed by land and wetland ecosystem. Marine species have wider distribution in the Indo-Pacific region whereas land and freshwater species have patchy; restricted and isolated distribution. The species of Paludomus, Cremnoeonehus -etc. are restricted to streams either in Western Ghats or North-east India. Similarly majority of land species are restricted to tropical rain forest ecosystems. Thus the diversity is more in Western Ghats and North-east India.

In the absence of a comprehensive data on marine molluscs it is too premature to attempt an estimation of species diversity and the extent of endemism. The available data indicates the existence of about 3370 species, but it may be actually more.

Introduced Species

I There are not many introductions as far as molluscs are concerned. The giant African snail, Aehatina juliea Juliea (Bowdich) was intrdduced by W. H. I Benson in 1847. He collected a few specimens from Mauritius and introduced a few in Botanical Gardens, Calcutta and a few in a gardert in Shimla. The latter specimens had died, but those released in Calcutta have multiplied and spread to other states of the mainland. During the Second World War, Japanese soldiers had introduced this snail in South Andaman which has now dispersed to Nicobar Islands also. The species has successfully spread to almost all states, except sub-himalayan range, semiarid and arid zones. It became a pest to agri-horticultural crops where ever it occurs. When chemical measures could not control the snail, a carnivorous snail Euglandina rosen was introduced in the Islands. But fortunately it did not survive. It needs mention here that the same snail E. rosea has been responsible for the extinction of certain small endemic snails in Hawaii. However, Achatina fl/lica is now identified as a potential foreign exchange earner for us as there is a demand for this snail in French markets. Andaman and Nicobar Islands can provide rich breeding grounds and collecting centres for this.

A number of sedentary marine organisms are carried on inadvertently on the hulls of maritime vessels and ships from their original area of distribution to foreign locations. A central American species, Mytilopsis sallei, has spread beyond its original home. The species was first observed in 1967 in Southern Lighter channel in Visakhapatnam harbour and by 1970 it had spread to other areas in the harbour. It was later reported from Bombay harbour (in 1975) and Kakinada Port (1985) (Satyanarayana Rao et aI, 1989). The species was not a fouler in its original home, but in India it has estflblished itself in the fouling communities.

Human-Mollusc Relationships

Man has been attracted by molluscs from prehistoric times because of their aesthetic and gastronomic values. But unlike in vertebrates, man has not contributed anything to the diversity of molluscs. He has been exploiting them from their natural habitats and putting them to different uses. He has been inadvertently responsible for the dispersal of certain species. The common garden slug, Laevicaulis aUe has its present wide, cosmopolitan distribution since it was carried along with plants. A species of slug, Kasperia sp. which is a pest in potato gardens in Nilgiris had probably been introduced along with potato crop.

Endemic And Rare Molluscs

The malacofauna of India shows some special and distinctive features. These are more evident in non-marine molluscs than in marine molluscs. Against an estimated total of 4000 species and 133 genera of operculate land snails of the World, India's share is aqout525 species falling under 32 genera. The estimates for pulmonate land snails and slugs of the world are 667 genera and 15000 species, with 104 genera and 950 species occuring in India. The land operculates of India include a number of zoogeographically Significant genera such as Cyclophorus, Diplommatina and Alycaeus, which are typical to oriental region and have number of endemic species. Majority of these species are distributed in penin~ular plains and Western Ghats. The pulmonate snails of the genera, namely, Macrochlamys, Sitala, Kaliella, AriopJulltta Girasia, Austenia, Sesara, Sophina and Durgella have a number of endemics confined to tropical rainforest ecosystem in North eastern India and Western Ghats. Boysia, Lithotis, and Camptonyx are endemic to India. These are represented by old collections, made during the last century and their present status is not known. The unique example of Indian land molluscs is the imperial snail of India, Hemiplecta basi/ellS, which is common in the teak forests of Western Ghats.

Besides the land snails mentioned above, there are a few genera of slugs such as Mariaella, lncillaria, Kasperia and Anadenlls which occur at higher elevations and are typical to Oriental region with their major distribution centres in India. The diversity in freshwater molluscs is comparatively poor than that in land or marine molluscs. Against the estimated 8,765 species of freshwater molluscs in the world, there are about 300 species in the Indian subcontinent. A large number of these (213) were reported from India proper. A few endemic and monotypic genera are reported, namely, CremnoconcJlIIS (Western Ghats), Mysorella (monotypic genus from Peninsular Plain), Mainwaringia (monotypic genus from Gangetic delta and esturies of Gujarat extending up to Vietnam). A few families of bivalves have contributed a single genus or species to freshwater fauna, namely Scaphllia (Arcidae), Novaclllina (Solenidae), Tanysiphon (Glauconomidae) and Modioills (Mytilidae) all living in the Gangetic delta. These provide interesting material for evolutionary Fd biogeographical studies. / Indian freshwater bivalves have special features in having two fJmes, namely Unionidae and Pisidiidae which are of great antiquity. The fabily I Aetheriidae, whose representatives are popularly known as freshwater oysters, has a restricted distribution in South India. Endemism in Indian molluscs seems to be more pronounced in freshwater ecosystem. Generic endemism is very much significant being at 66 per cent only, but 41.8 per cent of species are endemic. In land molluscs, about 33.5 per cent of species are endemic with a low (7.14) per cent of generic endemism. No attempt has been made to estimate endemism in marine molluscs as systematics of several families are in a fluid state. The present state of knowledge does not prOVide any clue to the threatened species of molluscs. Many of the species were not recollected after their original discovery or their first collection. In this connection the global scenario is not in any way better. There is no documented data on rate of mollusc extinctions.

Van Bruggen and Wells (1992) mentioned that as per World Conservation Monitoring Centre about 170 species of molluscs had become extinct since 1800 A.D. The 1990 IUCN Red List recorded 425 species of molluscs under the threatened category.

Authentic data on the status of various species of molluscs is not readily available. Our recent surveys have shown that species which were once abundant and easily available are hard to find now in their habitat. In Andaman and Nicobar islands, 71 of the known 101 species are endemic. Many species collected last were, at the end of the ninteenth century (Subba Rao and Mitra, 1991). Although it needs confirmation, some of the species in the Andaman and Nicobar Islands are either rare or have probably become extinct. Out of the 85 species for which specimens are available, 39 species are represented by the collections made during the later half of last century. Their present status as viable species is doubtful. The old collections from the Islands have originated from localities around Port Blair, Mt. Harriet, Great Nicobar, Car Nicobar, etc. which were easily accessible at that time. The localities from where Roepstorff, Godwin-Austen, Stoliczka and others made collections during the last century have undergone changes during later years. Land molluscs are highly susceptible to environmental changes and it is presumed that at least a few species may have been wiped out of their habitats. But in the absence of the any concrete evidence we cannot brand them as extinct. Intensive surveys are needed to establish the fact that species (25) which have not figured in recent collections, are either rare or extinct.

In Meghalaya, 223 species of non-marine molluscs were recorded but recent sampling could yield only 131 species. The fate of about 92 species is hard to explain. Among freshwater molluscs there are a few species which have not been collected second time during the last 100 years. Lithotis tllmida (Blanford, 1870) which was recorded from Pune district, Maharashtra has not been collected again. Arcidopsis footei (Theobald, 1876), a bivalve was not collected after 1912. Another bivalve commonly known as freshwater oyster, Acostaea (Pselidomlllleria) dalyi (E. A. Smith, 1898) has not been collected after its original discovery. A very small population of this species was reported last year in Bhadra River, near Kalsa, Karnataka. All the above three species are endemic to the Western Ghats.

Value

The value of molluscs to man are manifold. Majority of molluscs belonging to classes Gastropoda, Bivalvia and Cephalopoda have consumptive and productive uses. Land snails are not of any consumptive use in India. But there are 19 species of freshwater molluscs, both gastropods and bivalves, which are eaten in eastern India and more than two dozen species of marine gastropods, bivalves and cephalopods, which are of edible value. Majority of these are consumed in India, while some are exported out of the country. Squid fishing has developed into a very profitable industry along Gujarat coast.

Freshwater mussels, pearl oysters, turban and top shells are sources of mother of pearl. Fresh water mussels were once popularly used in the manufacture of buttons and a prosperous shell products industry flourished in North Bihar. Shell fisheries in North Bihar are dependant mainly on three species namely Parreysia (Radiatula) caerulea (Lea), Parreysin (Parreysia)favidens (Lamarck) and Lame/lidens corrianus Lea. Shell Button Industries, Mehsi, East Champaran Dist., handles Rs. 20 lakhs worth finished products annually (Banerjee & Satish, 1988).

Productive use of molluscs is more pronounced in marine molluscs. In recent years international trade in ornamental shells has been on the rise. Sea shells and cuttle bones are exported to various countries, namely, Saudi Arabia, U. S. A; Malaysia, U. A E., France, etc. Sea shells are used in the manufacture of ornaments and household articles such as table-lamps, ash¬trays etc. The finished shell products are sold either in the local market or exported to foreign countries. Shell lime industry depends completely on sea shells. These are also used in the poultry feed additives. Some of the/shells such as Villorita cyprinoides and Villorita cornucopin are used as ra"J'material in the cement and rayon industry. Recent investigations have flhown that some of the molluscs are potential sources of biomedical compounds.

Besides the direct values mentioned above, molluscs have an important role in the ecosystem. They draw a small quantity of calcium for the formation of shell from their environment and release it back into the environment. Molluscs play an important role in litter decomposition in the terrestrial ecosystem and formation of organic detritus in estuaries.

Threats

Molluscs, like all other animal groups are threatened by habitat alteration and indiscriminate exploitation by man. The impact of habitat disturbance on mollusc populations is not known because of lack of supporting data. But it is possible to draw certain inference. Molluscs, especially non-marine forms are charactrised by low mobility, small populations, patchy and isolated distributions. These are very sensitive to environmental changes. As mentioned earlier some of the species may have become either rare or endangered, as they do not figure in recent samples. The shrinkage in wetland ecosystem reduces the opportunity for colonisation of molluscs. The genera Camptoceras which was collected from the Ganges and its tributaries has become rare in its type locality. Majority of the important marine molluscs are associated with coral reef ecosystem, which is sensitive to any external disturbance. It was reported that the construction of Fishery Jetty at Phoenix Bay, Port Blair has adversely affected the pearl oyster, Pinctada fllcata, which was once common in that area. Dredging operations in the lagoon of Minicoy caused siltation adversely affecting the population of Tridacna maxima (see Patterson Edward & Ayyakkannu, 1992).

In the Gulf of Kutch, pearl oyster population has been on the decline. It was mainly due to habitat disturbance, such as heavy lifting of sand and rock from the natural pearl oyster beds for construction work, lifting of stones by local fishermen for wada fishing and use of DDT and other chemicals by traditional Pagadia fishermen to catch the fish. The major threat to molluscan diversity is in the form of over exploitation and collection of undersized specimens. Freshwater mussels are sources of the mother of pearl, which was once popularly used in the manufacture of buttons. There was once prosperous shell products industry in North Bihar. The number of industrial units have declined from 350 in 1940 to 84 at present. The decline in the number of these units is mainly due to the non¬availability of raw material, of three species as mentioned earlier. These bivalves are collected from the Ganges and its tributaries. The available statistics indicate that there is deplection of natural populations of these mussels.

Sea shells are needed in large quantities by the domestic shell craft industry. Shell craft industry selects those shells which have saleable value and discards others. In the process, a large resource uprooted from its place of occurrence is just discarded and thrown as waste. It was seen that one shell craft industry located at Bombay discarded about 200 tons of sea shells as they do not conform to the standards of the traders. Clam shell deposits are exploited locally in estuaries (Bahuda) of Orissa, Kakinada (Andhra Pradesh) and Kundapur (Kamataka). There is a large scale exploitation of Meretrix meretrix and Meretrix casta at several coastal places. Subfossil deposits of Meretrix is collected in bulk quantities from Talsari river mouth in Orissa and transported to interior places in West Bengal for use in the poultry feed. In Kundapur estuary, Karnataka,

M. meretrix, M. casta and Papllia malabarica are dredged regularly and sold to pulp and rayon industries.

If the exploitation of molluscs continues at the current rate without assessing the impact on their populations, soon many species will be wiped out in their natural habitats. The problem of overexploitation creates further complications as there is dearth of essential life history and biological information for a number of species used in trade. Villorita cyprinoides and Villorita cornucopia are two bivalves with restricted distribution in Kerala and Goa. Both the species are collected alive and the shells are used as raw material in the cement and rayon industries.

Commercialisation of sea shells has been on the rise and it has led to indiscriminate collection of sea shells. Since there are no strict regulations in many parts •of the country, governing the collection of shells, molluscan resources are treated as "Open access resources" or public goods. At several easily accessible coastal places and at places where tourists frequent, populations of certain common species are on the decline. For example, Arnalda ampla, the ivory white olive was once common on the Digha beach, but it has become almost rare now. It was collected locally and used in the preparation of curios, necklaces etc.

Marine species are however, not as much in danger as their counter-parts on land or in freshwater. Many of the marine species have a longlived pelagic larvae and hence they are widely distributed in the Indo-Pacific. The well-known tiger cowry, Cypraea tigris has its range of distribution extending from the coast of East Africa to Central Pacific. Cones and scorpion conchs are also distributed throughout Indo-Pacific. However, all the species are not uniformly distributed within their ranges of distribution. Populations are concentrated in areas which offer ideal ecological niches.

Gaint clams, which are hermaphrodites, have 9 to 12 days of larval life, and consequently their distributions are also limited. Although majority of the marine gastropods have a freeswimming veliger stage, there are certain gastropods, in which the development is direct, i.e., there is no larval stage. Some marine prosobranchs especially Neogastropoda have no free swimming larvae. The sacred chank of India is one such species. Its distribution is very much restricted. It occurs in the Gulf of Mannar, Gulf of Kutch and Andaman and Nicobar Islands. Even in these areas of its occurrence, it has a localised distribution. Absence of a free swimming larval stage, coupled with long span of life make these molluscs more vulnerable to the adverse impacts of human activities.

Many of the species as mentioned above are harvested indiscriminately without realising the impact of over-exploitation on the species and on the ecosystem. Recently Rama Raju (1991) in an interesting study has brought out the impact of large scale destruction of molluscan fauna on the ecology of Kolleru Lake in Andhra Pradesh. Gastropods were removed in large quantities from the Lake for supply to prawn culturists, who use them as prawn feed. It has created an adverse impact on the duck and bird population for whom molluscs are a source of food.

There is no authentic data on the threats to molluscan fauna in the Indian seas. But it is possible to draw lessons from situations' prevailing elsewhere. Over-exploitation has adverse effects on the populations of commercially used species. It was observed that intensive exploitation has led to the disappearance of the pearl oyster Pinctada margaritifera from some Polynesian Islands. Ornamental shell trade is causing depletion of local populations in many Pacific Islands, Philippines and on the Kenyan coast.

Conservation

The declaration of Gulf of Mannar, Gulf of Kutch and South Andaman as Biosphere Reserve/Marine National Parks affords protection to marine molluscs. There are also some regulations particularly governing the collection of shells. In Andaman and Nicobar Islands, nine areas are demarcated for collection of shells. A closed season of two years is allowed in all the areas to permit replenishment of population. The collection of undersized specimens of Trochus (less than 10 em) and Turbo (less than 6.5 cm diameter) is prohibited. The catches are inspected by the local officials of the Fisheries Department before permitting the export of shells for sale.

In the Gulf of Kutch shell fisheries are under the control and supervision of Department of Fisheries, Government of Gujarat, whereas the Marine National Park is under the control of Gujarat State Forest Department. There are regulations governing the collection of sacred chank (Turbinella pyrum), Window-pane oyster (Placenta placenta). The rights to collect shells are leased out by the State Government.

There is prohibition to collect undersized specimens-61 mrn in the case of chank, 11.4 cm in the case of window-pane oyster. Collection rights for shells are leased out by the government and the leases in their anxiety to make as much profit as possible try to extract maximum mileage out of the deal. In spite of regulations very often, undersized specimens are also collected and sold. A number of shells which are collected with tradeable and desired species are just discarded and thrown on the shore. As there is no close monitoring of the fishing and no punitive measures, valuable resources are thus wasted (Sarvaiya, 1987). There was once a good pearl fishery, which was a state monopoly. But it is almost non-existent now. The decline in the populations of commercially important species are reflected in their dwindling catches. The lesson are clear that conservation of molluscs should be accorded top priority in the Gulf of Kutch to avoid further loss of this valuable resources.

In the Gulf of Mannar also, there are important shell fisheries like Chank fishery and Pearl oyster fishery. There are regulations governing the collection of shells and shell fishery.

Future Action

Althouth several habitats of molluscs are declared as protected, there are no strict rules and regulations regarding collection of molluscs. Hitherto, the emphasis has been on terrestrial habitats. The importance given to conservation of Wetland ecosystem affords some protection to non-marine aquatic molluscs. There is a large scale exploitation of freshwater molluscs in eastern India. It is essential to initiate some control measures to protect the natural populations. Since molluscs serve as a poor man's diet, a complete.... halt to their collection may create socio-economic problem. Farming techniques have to be developed in case of freshwater molluscs also to make them available to local communities for consumption.

There should be a monitoring of shell collection in most productive and diversity-rich centres of the country. Shell collecting should be restricted to only abundant and common species, guidelines for collection of shells have to be prepared and the same to be made popular among the collectors. Hitherto, no mollusc has been included in the Wildlife (Protection) Act, 1972. Indian Trade classification lists a number of mollusca that are exported out of the country. An illustrated guide book of all the exported items, with the source species, should be prepared. One such book on "Squid and Cuttlefish" has been prepared by the Marine Products Export Development Authority. There should be proper monitoring, and permission to trade should be given to only those items recommended by the experts on the subject.

Selected References

Banerjee, S. R. & Satish, M. S. 1988. Mussel shell products industry in Bihar. Science Reporter, May, 1988. 286-287.

Van Bruggen, A. C. and Wells, Susan M. 1992. Alan Solem Memorial Symposium on diversity and Conservation of Molluscs: Key note Lecture. Abstr. 11th Intern. Malcol. Congr. Siena (F. Giuste & L. G. Manganelli eds.) : 166-168. Patterson Edward, J. K. and Ayyakkannu, K. 1992. Conservation of edible bivalve resources of India. Abstr. 11th Intern. Malcol. Conr. Siena (F. Giuste & L. G. Manganelli eds.) : 184-185.

Rama Raju, T. S. 1991. On the large scale destruction of Molluscan population of Kolleru Lake and its likely impact on the lake ecology. National Workshop on Kolleru Environment Information System. October, 1991, Hyderabad (Abstract). Rao, T. S. S. 1987. Environment Productivity and Management of the Coastal Seas off Karnataka. In : Karnataka, State of Environment Report 1985-1986 (ed. Cecil J. Saldanha) : 93-103.

Sarvaiya, R. T. 1987. Commercially important molluscs of Saurashtra coast : Conservation and Development. Fishing Chimes., 7(9) : 49-53. Sarvaiya, R. T. 1989. Molluscan Exports from India with Reference to Gujarat State. Fishing Chimes., 9(3) : 43-45. Satyanarayana Rao, K., Srinivasan, V. V. and Balaji, M. 1989. Success and spread of the exotic fouling bivalve Mytilopsis sallei (Recluz) in Indian Waters. Exotic Aquatic Species in India (Ed. M. Mohan Joseph), Special Publication, 1 : 125-127 (1988). Subba Rao, N. V. 1991. Mollusca. In : Animal Resources of India: 125-147. Zoological Survey of India, Calcutta. Subba Rao, N. V. and Mitra, S. C. 1991. Land Molluscs of Andaman and Nicobar Islands. Zool. Surv. India. Dec. Paper No. 126 : 1-88.

Mollusca

This is an extract from ANIMAL RESOURCES OF INDIA: Protozoa to Mammalia State of the Art. Zoological Survey of India, 1991. By Professor Mohammad Shamim Jairajpuri Director, Zoological Survey of India and his team of devoted scientists. The said book was an enlarged, updated version of The State of Art Report: Zoology Edited by Dr. T. N. Ananthakrishnan, Director, Zoological Survey of India in 1980.

Note: This article is likely to have several spelling mistakes that occurred during scanning. If these errors are reported as messages to the Facebook page, Indpaedia.com your help will be gratefully acknowledged.

Introduction

The Molluscs are of great antiquity and diversity. By the time the first fossils were known in the Cambrian period, about 600 million years ago, molluscs were already distinguished into their major classes. It led malacologists to conceptualize the existence of a soft-bodied ancestral archetype mollusc in the Pre-Cambrian period. The ancestral mollusc, which crawled about on rocks and other hard substrata of the oceans gradually passed through transitional turbellariform stage, transitional molluscan stage and evolved into the advanced molluscan stage by the Cambrian period.

Molluscs are a structurally heterogeneous group, since a slug is strikingly different in structure from a freshwater mussel or from an octopus or a snail. The shell, by which majority of the molluscs are known, is absent in several forms. A mollusc has to be recognised on the basis of a combination of traits or characters. When a number of such characters are involved in the identification, the relative importance of each such character becomes variable, depending on the weightage given to that particular one. It has posed problems in the' classification of Phylum Mollusca.

The term 'Mollusca' was first adopted by Linne (1757), but the concept of the group developed by euvier (1791) approximates to modem ideas. According to gross morphological, anatomical and biological features, Phylum Mollusca has been divided into three subphyla and seven classes, which are as follows :

In numerical abundance the phylum is second only to Arthropoda (not considering the microscopic Nematoda). Estimates of the number of species in Mollusca vary between 80,000 to 1,00,000. According to one estimate there are 50,000 species of gastropods, 15,000 species of bivalves, 500 species of polyplacophorans, 400 species of cephalopods, 300 species of scaphopods, 130 species of apalcophorans and 5 species of monoplacophorans. A more conservative estimate gives the number as 31,463 marine 8,765 as freshwater and 24,503 terrestrial species (Winckworth in Eales, 1949).

Molluscs are soft-bodied animals and have colonized all possible habitats, extending from deep seas to highest altitudes (4500 m). They are, however, more abundant in littoral zones of tropical seas. The classes Apalcophora, Polyplacophora, Scaphopoda and Cephalopoda are exclusively marine and account for 2% of the total living species. The two large classes, namely, Gastropoda and Bivalvia have extended into freshwater and the fonner even on to land. The two classes together constitute 98 % of the known living molluscan species.

Molluscs have successfully adopted to different ecological conditions. They act as important components in the production of biomass. They are the fust living creatures to have hard shells, and the earlier man was perhaps attracted to these shells. The association of man and molluscs dates back to prehistoric ~mes as evidenced by their remains in Mohenjadaro, Harappa and others places. A large number of shells were unearthed in the kitchen middens of ancient men. Besides the aesthetic appeal of their shells, the soft parts of molluscs are edible. Some of the molluscs can be used as potential sources of biomedical compounds, which are used in the manufacture of drugs.

They aiso produce commercially valuable products like pearls and raw material for the shell-craft industry. Molluscs support viable fisheries in several countries, including India. Shells, snails, cuttle-fishes, squids, etc. are foreign exchange earners for India. Certain snails serve as intermediate hosts of several trematode parasites, spreading diseases in livestock and man. They choke the filtered water pipe systems and water inlets of coastal thermal power plantsr Shipworms and piddocks bore into marine timber structures causing heavy losses. A few of the land snails, when they occur in abundance, pose a serious threat to agri-horticultural and commercial crops.

Historical Resume

Molluscs were collected in the beginning oilt of amateurish love or cwiosity of shells. Collections were made at random and preserved for further study. Collections had accumulated through tJte efforts of individuals, who were otherwise engaged in the expeditions or topographical surveys. Their attention was naturally drawn to land molluscs. The incidence of schistosomiasis after the First World War, led to a search for its possible intermediate host in India, which in turn promoted studies on the taxonomy and distribution of freshwater molluscs. The launching of RIMS Investigator in 1881 A.D. formed an important milestone in _the study of marine molluscs. Thus studies were initiated on land, marine and freshwater molluscs -of India even before the establishment of the Zoological Survey of India.

i) Pre-1900

Studies on Indian molluscs were promoted by the Asiatic Society of Bengal (1784) an4 the Indian Museum, Calcutta (1814). The Journal of Bombay Natural History Society started in 1886 provided yet another avenue for Indian malacologists to report the results of their researches. The scientific staff attached to the Palaeontology Division of the Geological Survey of India also contributed to the knowledge on Indian molluscs. The successive Superintendents of Madras Government Museum undertook sevcral dredging operations in the Gulf of Mannar and supplied material for research.

Although the collection of molluscs had started in the later half of the eighteenth century, it was occasional and sporadic in nature. It took another few decades for a matacologica1 publication to appear. Benson, in 1830, was perhaps the first author to publish a scientific paper on Mollusca. Between the years 1830 and 1865-Benson published a total of about 90 papers dealing with the land and freshwater molluscs of the Indian subcontinent. During the later half of the nineteenth century many malacologists have emerged on the scene: Beddome (1875-1906), Blanford (1860¬1904), Godwin-Austen (1874-1922). Hutton (1949), Melvill (with Sykes and also Standen, 1888-1904), Nevilll G. &H. (1871-1888), E. A. Smith (1878-1903). Stoliczka (1969-1873) and w. Theobald (1859-1889).

Col. R. H. Beddome was essentially a botanist, who was appointed in the Forest Department. He collected good samplcs of molluscs, especially land operaculates from the hill ranges and forests of Central and South India. All his collections were studied by W. T. Blanford, with whom he published a Fauna volumc. After his death all the collections were donated to the British Museum (Natural History), London.

w. T. Blanford (1832-1905) was primarily a geologist attached to the Geological Survey of India. He had explored a large part of the subcontinent and had acquired rust hand knowledge on the distribution of animal life. He publishcd a series of about 40 papers, either himself or in collaboration with his brother, H. F. Blanford and contributed a total of about 400 printed pages on molluscs. He was responsible for the inception of official "Fauna of British India" series to which he contributed five volumes on vertebrates. However, he could not complete the fust volume that he had begun on land and freshwater Mollusca, Which was left to be completed by his life-long friend, Col. Godwin-Austen.

Ferdinaa,d Stroliczka, who came to India in 1862, had wider zoological interest and could not concentrate much on molluscan studies. During his Second Yarkand Mission (1873-74) and several other expeditions, he collected a number of molluscs which were studied by Nevill and others. He was the first malacologist to draw attention to anatomical details through his publication on the specie$ of Onchidium. The g'ood work that he contemplated did not progress much.

The fast effort to consolidate the then existing malacological knowledge was found in Hanley and Theobald's Conchologia Indica (1876) which was aimed at facilitating the labours of those who may aspire to produce a more perfect conchology. About 1885 species classified under 88 genera of land and freshwater molluscs of India and adjacent countries were enwnerated in that well illustrated work.

In 1878, Geofferoy Nevill (d. 1885) who was Assistant Secretary and Librarian in the Indian Museum, published the fast part of his 'Hand List of Mollusca in the Indian Museum'. followed by part n in 1885. Although Nevill introduced many nomen nuda and thereby caused confusion his works gave an improved classification and exact localities of each collection. In addition to these, Nevill along with his brother, H. Nevill brought out a series of papers on marine and freshwater molluscs. Hiscontributions on molluscs of Bay of Bengal, Sri Lanka, Ladakh and Burma.contain a number of new species, largely of gastropods.

The collections in the Indian Museum which now fonn a part of the National Zoological collections were well maintained and catalogued by Nevill. After his retirement the collections have passed through many hands and several species catalogued by Nevill were lost for ever to Science.

In 1889, Theobald published the first part of Index of Genera and Species of Mollusca in the Hand List of the Indian Museum, Calcutta.

The most valuable contributions to knowledge on land molluscs were by Godwin-Austen (1834-1923), who took up study of molluscs at the instigation of Dr. Blanford. From the time he came to India in 1851 and till his death Godwin-Austen took keen interest in the study of molluscs and developed an intimate and extensive knowledge on the subject. He explored the great mountain ranges of Baluchistan and the sub-Himalayan ranges starting from Kashmir on the west to Garo and Naga Hills in the east and participated in the Dafla Expedition 1874-75. Besides many scientific papers on land molluscs, Godwin-Austen published volumes on Land and Freshwater Molluscs of India (1882-1910). He studied Zonitidae and land operculates with great acumen and illustrated profusely with his own drawings. His publication on the genus Glessula was very comprehensive and authoritative. He described about 450 new species mostly belonging to the families Ariophantidae, Cyclophoridae, Diplommatinae etc.

Throughout the period the stress had been mainly on the collection and study of land molluscs, occasionally including freshwater forms. In the last two decades of the century attention was diverted to marine mollus~s. The publication of Alder and Hancock's (1866) monumental work on Opisthobranchs of South India and Sri Lanka was an important step in that direction. There was a general build up of interest in marine biology which heralded the formation of a Committee by the Asiatic Society of Bengal in 1871. It included distinguished biologists such as Blanford, Stoliczka, Anderson, Oldham and Woodmason.

It led to the establishment of the Marine Survey Deparunent in 1874. J. Woodmason, a deputy of the Trustees of the Indian Museum undertook pioneering deep sea biological investigations in the Andaman and Nicobar Islands, even before the establishment of the Department His material was studied later by Preston. After Alder and Hacock, G &H. Nevill (1871) took more interest in the study of marine molluscs. An important aspect in the study of Indian Ocean Malacology was the work of the Royal Indian Marine Survey Ship, 'Investigator' which was launched in 1881. Natural History Notes from RIMS Investigator were initiated in 1885 and the frrst few appeared in the Journal of Asiatic Society of Bengal and later a maximum number had appeared in the Annals and Magazine Natural History, London. E. A. Smith (1889¬1905) had enumerated a total of about 400 species based on Investigator material and of which 176 species were described as new to science. Smith alone had been the author of l62 species. lllustrations of the Zoology of RIMS Investigator pertaining to Mollusca were published in 23 supplements from 1898 to 1909.

Abercrombie (1893, 1894) collected and studied molluscs from the Bombay coast. His collections, which consisted of about 400 species, were originally donated to the Manchester University Museum, but now found in the British Museum. Melvill (1885-1928) in collaboration with Abercrombie (1893), Sykes (1897) and Standen (1898) described molluscs from the coasts of Bombay, Andamans and Madras. Melvill Standen are particularly remembered for their studies on the marine molluscs of the Persian Gulf and the Arabian Sea, which were collected by F.W. Townsend between 1893 arid 1915, while laying the Telegraph cables.

About 2000 species (of which 600 new species) were enumetated from Townsend's collection alone and altogether Melvill is credited with the authorship of about a thousand species. Many of his types are now available in the British Museum, Cardiff Museum and Manchester Museum.

Thurston (1890, reprinted in 1894), Superintendent of the Madras Govt. Museum, published an account on the. molluscan fauna of ;Pearl and Chank fisheries in the Gulf of Mannar.

The contributions, during the period, in general, included faunal lists, taxonomy often with anatom,ical details, distribution and field ecology of mostly land molluscs, and to a lesser degree of marine and freshwater moluscs. Most of the collections, with the exception of those studied by Nevill and E. A. Smith, had been deposited in the British Museum, Cardiff Museum, Manchester and Cambridge University Museum and other museums in England.

ii) 1901-1947

It is the most productive and significant period in the history of Indian Malacology. The establishment of the Zoological Survey of India in 1916, gave an impetus to organized malacological research. The period is marked by the presence of luminaries of Indian MaIacology. like Preston (1903-1916), Annandale (1907-1925), Hornell (1910-1951), Prashad (191s.:-1934). H. S. Rao (1923-1941), Seshaiya (1928-1949), \Vinckworth (1926-1940) and others.

Indian Museum was still playing prominent part by encouraging malacologial research. In the year 1907, Thomas Nelson Annandale, the then Superintendent initiated two new scientific journals, Records of the Indian Museum and Memoirs of the Indian Museum. Several important fmdings had been published through these two journals. S. W. Kemp, Asstt. Superintendent of the Indian Museum lead the Abor Expedition in 1911-1912 and brought tO'light ~veral interesting land molluscs, which included a total of about 45 species of operculates (Cyclophoridae). The collections were studied by Godwin-Austen (1914) and E. G. Ghosh (1913).

The studies on land molluscs, which culminated in the publication of three Fauna volumes (Blanford &Godwin-Austen, 1908; Gude, 1914, 1921), were on the decline and the main thrust had shifted to freshwater molluscs.

The incidence of schi,stosomiasis in the troops returning from South Africa during World War prompted the authorities to take up a study of the etiology of the disease and its possible intermediate host in India. Annandale was entrusted with these investigations, and in his search for the intermediate snail host he travelled as as far as Seistan in Eastern Persia and to several places in India. Thus he was induced to take up studies on the taxonomy and distribution of freshwater gastropods. Annandale made significant contributions to freshwater malacology and had been the pioneer in medical malacology. He had also studied the molluscs of hill streains, lakes and published a monograph on molluscs of the Chilka Lake (1924). Annandale (1923) had reviewed the advances in our knowledge of the fauna of the fresh and brackish waters of India. He had provided material for the revision of many families of freshwater moiIuscs and revised the most common families, Vivaparidae and Lymnaeidae in collaboration with Sewell (1922) and Rao (1925) respectively.

Prashad and H. S. Rao, who had their initial training under Annandale took to serious study of molluscs. Prashad was a giant among contemporary malacologists. He investigated the anatomy of several freshwater gastropods and bivalves and revised some families. His contributions on the families Pilidae,.Viviparidae, Unionidae and Corbiculidae are widely referred and followed by later workers. His other significant works on marine molluscs include the revision of the family Nuculanidae and a monograph on the bivalves of the Siboga Expedition. H. S. Rao made useful contributions to the comparative anatomy of freshwater gastropods and on the growth rate of some commercially important species. Hora (1925, 1926 &1928) made some important observations on the aestivation of the succineid molluscs and land slugs.

Besides those working either in the Zoological Survey of India or on the material supplied by the institution, there were a few Zoologists, who devo~d their time to the study of land or freshwater molluscs. Important among them were, E. N. Ghosh (1912-1920), who studied the anatomy of a slug and some bivalves, and Seshaiya (1928-1949), who investigated the style sacs and the anatomy of certain freshwater gastropods. Other important contributions were" Germain's Catalogue of the Planorbidae of the Indian Museum (1921-1922), Bahl's studies on Pila (1928) and Bhatia's work on Anadenus.

The studies on marine and brackish water molluscs had received considerable importance. Molluscs of Chilka Lake, and of est~aries and brackish waters along the east coast were described in a series of papers by Preston (1908, 1914, 1916), Annandale &Kemp (1916-23) and Prashad (1927). Preston also described several new species from Andaman and Nicobar Islands. Panikkar and Gopala Aiyar (1939) dealt with brackish water animals. Paul (l924) recorded the growth and breeding of certain sedentary organisms. "

During the period, Zoological Survey of India had been the nodal agency for malacological research. It established a good relationship with museums in Europe. The Royal Natural History Museum, Brussels was one such institute which had close links with the Survey. Indian collections of chitons and cephalopods were studied by Leloup (1926-1953) and Adam (1939) of that institute respectively. Massy (1919) studied the Investfgator material of Cephalopods and reported Bathyteuthis abyssicola from a depth of 2000 fms. Eliot (1906, 1919) reported on the nudibranchs of the east coast of India.

Shell-fish resources were given their due share of attention. James Hornell, the Director of Fisheries to the Government of Madras from 1907 to 1924, had highlighted the edible value and commercial importance of molluscs. He contributed a series of papers on vario~s aspects of Shell¬fishery. Marine Zoology of Okhamandal (1909), Sacred Chank (1914) and its races (1916), edible molluscs of Southern India (1917) and common molluscs•of Southern India (1922) were some of his significant contributions. Rai (1928, 1932) gave an account of the shell-fishes of West coast. Biology and fishery of the edible oyster were studied by Awati and Rai (1932). For the fast time an account of the pearl oyster of Indian waters was given by Prashad and Bhaduri (1933). At the instance of Dr. Sewell, the then Director, Zoological Survey of India, H. S. Rao (1939) "made a special study of shell-fisheries of Andamans and reported on the breeding biology, bionomics, distribution etc. of Trochus. Moses (1927, 1940, 1947 and 1948) dealt with the fIShery of Placuna and Cephalopods of the Gulf of Kutch. Devanesan (1940, 1944) reported on the bionomics of sacred chank: and shell-fish fished by Lady Goschen" (1927-1930).

Gravely's (1941) work on shells and other animal remains found on the Madras beach is still useful in the identification of many species of marine molluscs.

Vredenburg, whose contributions to the knowledge of fossil molluscs are well known, had discussed variations in Pleurotoma conqener (1917, 1919) from the Andamans and also the peculiarities in the distribution of the family Doliidae (= Tonnidae). Prashad (1927) described a new deep water, Pyrula sewelli from the Laccadive Sea (180 fins.).

Harold Charles Winckworth, who was 'in the army as a surgeon had profound interest in natural history. He explored many localities along the east and west coasts of India, also Andamans and Sri Lanka. His contributions (1926, 1933) on marine molluscs, which included a few new species of chitons and nudibranchs were of systematic and descriptive value. Crichton (1940) enumerated the species of Madras coast.

The interest in molluscan studies had been on the increase and more number of workers were drawn to malacology. The advent of a number of investigators in the field of marine malacology had changed the scenario. Veerabhadra Rao emerged on the scene with his publications on opisthobranchiate molluscs (1936, 1937).

iii) 1948-1990

During the decade 1940 and 1950 there was a general slow down in the research activities of. the Zoological Survey of India which was the only institute then engaged in general zoological studies. All the old workers had made their exit from the scene of active research and the National Zoological collections had suffered a heavy loss due to Varuna floods in 1943. Besides, the collections were also shifted from Varanasi to Calcutta. All the efforts of'the scientists and staff of the Survey were diverted to the retrieval of damaged collections and their rearrangement. But elsewhere there had been a gradual proliferation of malacological research since scholars of various universities had been encouraged to take up studied on molluscs.

The establishment of Central Marine Fisheries Research Institute in 1947 had ~lso given a further boost up to malacological research. The realisation of the importance of marine timber boring organisms in our economy had made Forest Research Institute to sponsor schemes on these timber boring and fouling organisms. Thus institutional support to malacological research had been on the increase.

For the last four decades the successive scientists in charge of the Malacology Division in the Zoological Survey of India have been contributing to the knowledge of Indian Molluscs by undertaking their own research programmes and also by extending identification and advisory services to those working outside the Survey. Ray (1943-1969), the fast Officer-in-Charge of the Mollusca Section after independence, described a number of new species of land, freshwater and marine molluscs. Although he attempted revision of Indian mitres and Indo-Pacific cowries (unfmished), Ray's contributions were in general of systematic and descriptive nature. His book on molluscs of Maungmagan serves as a reference for synonymy and distribution of several marine species.

He brought out the importance of molluscs in chokage of fIltered water pipe systems and also as fossils. He was succeeded by Rajagopal (1965) who studied the systematics of shipworms in the initial years (1961, 1964 and 1973), but later published detailed accounts on the molluscs of Kashmir (1968) and the Chitons of Andaman and Nicobar Islands (1972) in collaboration with Subba Rao. Rajagopal and Mukherjee (1978) summed up our knowledge of the molluscs of Coromandel coast. Subba Rao, who is currently the head of the Malcology Division, had developed a team, which is studying the systematics, ecology and distribution of land, freshwater and marine molluscs. Thc investigations are aimed at filling up the lacunae in our knowledge. Since the systematics of land molluscs are well known. The present studies have given importance to their ecology and economics. Subba Rao (1975) conducted pestiferous snail survey and drew our attention to some important pestiferous snails and the' data collected under the programme of Pestiferous Snail Survey had formed the main bulk of the material of the technical monograph by Raut and Ohose (1984). Besidc, investigations were also carried out on the breeding and growth rate in some common land molluscs (Subba Rao et al., 1989).

Subba Rao and Mitra (1979) published a comprehensive account on the molluscs of the Pune district. Subba Rao (1989) has updated our knowledge on the freshwater molluscs of India and adjacent countries. His Handbook on Freshwater molluscs of India would serve as a valuable guide to all those interested in the subject. Malacologists in the Zoological Survey of India have prepared State ofArt reports on estuarine molluscs and on marine molluscs belonging to the families, viz., Mitridae and Donacidae. Current studies include inventorisation of malacofauna of different states of India. Roonwal (1962) and Das (1980) have studied marine timber boring molluscs, whIle Agarwal (1977, 1981, 1983) investigated the growth rate and biology of some common freshwater molluscs.

Among universities, Annamalai has been in the forefront of Il)alacologial research. From 1929 to 1960 under the guidance of Prof. Seshaiya and later under the direction of Prof. Natnarajan, malacological research assumed a' new significance. Ramamoorthi (1949, 1950, 1955, 1960) investigated the chromosomes, chemical embryology and aminoacid contents of some common freshwater gasttopods.

Meenakshi (1951, 1954, 1956) studied the physiology of digestion and aestivation in the common Indian apple snail. Cytological studies by Jacob (1958, 1959) and Natarajan (1972) are very significant. Govindan's investigations on neritids (1974) and Kasinathan's on cyclophorids (1979) have thrown light on the biology of these molluscs: Kasinathan and his associates have been studying the molluscs of Vellar estuary and biochemical prope~es of molluscan secretions (Kasinathan and Shanmugam, 1985, Rajendran and Kasinathan, 1987).

Studies on various aspeCts of molluscs were undertaken under the guidance of Prof. Ganapatiin the Zoology Department of Andhra University. Systematics,. biology, neurosecretion and distribution of wood boring molluscs were studied by Nagabhusan~ (1959, 1960) and Lakshmana . Rao and Ganapati (1959). Molluscan fauna of the Kakinada Bay were studied by Radhakrishna. Rao, Balaparameswara Rao (1975) and Sarma (1976) in collaboration with Ganapati (1968, 1964, 1968) have studied the interestitial fauna, biology of Cellana radiata and molluscs associated with marine algae in that order. The work that was started at the Andltra University had been continued at the Nagarjuna University fllst by Radhakrishna and later by Balaparameswara Rao and their students. After Ganapati, studies were carried out on histochemistry and histopathology of certain marine and freshwater molluscs under the guidance of Prof. Hanumantha Rao. Physiology of certain marine molluscs was investigated by Prasada Rao and his students.

Freshwater molluscs of Andhra Pradesh and the molluscs of mangroves in the Krishna estuary have been chosen for special investigations at the Nagarjuna University (Janakiram and Radhakrishna, 1984, 1987); Murthy &Balaparameswara Rao, 1977; Balaparameswara Rao and Sukumar, 1981, 1982; Rambabu et aI, 1987). The subjects like biology, physiology especially neurosecretion of marine, freshwater and land molluscs h~ve been pursued under the guidance of Prof. Nagabhushanam at Marathwada University.

Investigations were carried out on thiarids (Muley, 1975-78, Muley and Nagabhushanam 1975, 1977); pulmo.nates (Kulkarni and Nagabhushanam, 1975) and marine bivalves (Mane and Nagabhushanam, 1971).

Nagabhushanam built up an effective school of malacology and made significant contributions to knowledge on neurosecretion in molluscs (Nagabhushanam, 1974, 1977; with Lohgaonker, 1972; with Lomte, 1974; with Muley, etc.)

The fWlding of schemes on 'Marine timber boring organisms' by the Forest Research Institute of India had encouraged research on woodboring bivalves. Nagabhusanam (1953) studied the shipworms occurring in Visakhapatnam harbour. Sreenivasan (1959, 1961) 'investigated the functional morphology of Martesia. Important studies on shipworms were also carried out at the University of Kerala by Nair (1954-1966), Nair and Gummani (1957). Nair and Sarasawthy (1968). Studies on marine timber boring and fouling Inolluscs are being carried out by the Marine Wood Preservation Centres of Forest Research Institute at Waltair and at Goa, in which the investigations are led at present by Santha Kumaran (1983).

Satyamurti, curator of the Madras Government Museum has brought out three comprehensive volumes, two of them dealing with Molluscs of Krusadai Island and another one on land and freshwater mollusc collections in the Madras Govt. Museum.

On the west coast of India, Palekar (1955, 1957), Palekar and Bal (~955) published accounts on the destruction caused by marine organisms to timber. Durve (1960) studied the biology ofIndian oysters. Subrahamanyam et al (1949, 1951 and 1952) dealt with the marine molluscs of Bombay coast. Molluscs of Pirotan Island and Gulf of Kutch were studied by Gideon et al., (1957) and Kundu (1965) respectively. Significant contributions to our knowledge of molluscs of Gulf\of Kutch were made by Narayanan (1968, 1971 &1974) and Sarvaiya & Chaya (1983).

Physiology of molluscs was the subject of interest pursued at various Universities. Among these Calcutta had been in the forefront followed by Marathawada University. Ghosh (1960, 1962¬1964) thoroughly investigated the anatomy and embryology of Achatinafulica Bowdich. A number of important investigations have been carried out in the Ghosh's Laboratory at Calcutta University.

Reproductive systems of some important freshwater molluscs (Chatterjee, 1970), excretory struct~es (MandaI, 1971) biology of some parasitized.gastropods (Dasgupta, 1973) pathology of Achatina (Manna, 1975) ecological studies (Raut, 1981) were some of the important studies pursued under the guidance of Prof. K. C. Ghosh. At present malacological investigations are undertaken by Raut, Sur and their students. Raut and his students are carrying out ecological studies on certain common land and freshwater molluscs.

Physiology of some freshwater molluscs was the' subject of special interest to Sherbet and Lakshmi (1964), Saxena (1956, 1965) Raghupathiramireddi and Swami (1954, 1967, 1968) Patnaik (1968, 1971) and Pablaik and Ray (1966-68).

The establishment of Central Marine Fisheries Research Institute in 1947 had brought into focus the importance of marine molluscs in fisheries. Malacological research assumed greater significance and received much momentum. Commercially important molluscs have received more attention. Surveys were conducted and biological investigations •were carried out on a number of marine species. Virabhadra Rao (1951, 1953-1955), 1958, 1960) has been the leading malacol~gist who made significant contributions to shell fish fisheries artd opisthobranch molluscs. The studies by Abraham (1953) and Durve (1964) on Meretrix casta, by Nayar (1955) and Alagarswami (1966) on the Donax, by Narasimham (1969) on the Ark shell, by Silas (1968) on cephalopods have considerably enriched our knowledge on these molluscs. Bulletin no. 2S (eds. R. V. Nair and K. S. Rao) published by the Central Marine Fisheries Research Institute sums up our knowledge on molluscan fisheries. A number of studies have been encouraged on the biology, population density, fishery potential and culture techniques of economically important species of molluscs.

The good work that Durve had stared in ClvIFRI is being continued by him in the University of Udaipur, but concentrating on productivity in freshwater molluscs.

Since certain freshwater snails are important intermediate hosts of trematode parasites, occasionally helminthologists are also attracted to the subject and a few workers like Bali and Dutta (1978), Mohandas (1975), Biswas and Subramanian (1978) had investigated certain aspects of intennediate snail hosts.

Studies from Different Environs

The information on Indian molluscs is scattered in more than 4000 references involving more than 50 scientific and semipopular journals. It is impossible to get a coverage of all those references within such a short review. But in a very general way it can be said that a major part of these references deal with marine molluscs and cover Indian Ocean, which often may fall beyond the exclusive economic zone of India. A total of about 2380 references are cited for Indian ocean (Jones, 1971) which also include areas beyond Indian territory. During the last two decades an average of 25 references every year are estimated, thus making a total of about 3000 references on marine molluscs. About 555 references have been compiled with regard to freshwater moll~scs of India and adjacent countries (Subba Rao, 1989). The data on land molluscs is available in about 700 titles.

Malacological studies in India have started with land molluscs. In the beginning, studies on these molluscs were faunistically oriented. Extensive collections were made in the Himalayas starting from the Pir Panjal Range on the. west to Dafla, J aintia Hills etc. in the east. Collections were also made from the Peninsular India, especially in the Western Ghats. All the collections were studied by various malacologists during the pre-independence period. These studies have culminated in the publication of three volumes in the Fauna of India series. References to earlier publications on the subject can be obtained from these volumes (Blanford &Godwin-Austen, 1908; Gude, 1914, 1921). There are very few recent publications on land"molluscs of India.

Recent studies on land molluscs include those of Kashmir (Rajagopal & Subba Rao, 1971), Pone district (Subba Rao and Mitra, 1975); Orissa (Subba Rao et al., in press); Andaman and Nicobar Islands (Subba Rao and Mitra, in press).

There had been considerable interest in the study of molluscs of freshwater ecosystem. Preston (1915) published a Fauna volume which is useful as it gives first referrence and original description of several species. Important contributions were made after its publication by Annandale, Prashad, Rao, Nagabhushanam and his students. Up-to-date information and complete bibliography of freshwater molluscs has been provided by Subba Rao (1989).

Molluscs of the marine ecosystem have attracted a large number of workers from India and also abroad. A number of papers have been published on molluscs of different areas ip the Arabian sea. One of the recent publication on Bombay molluscs by Subrahmanyam efal (1949-52) records 308 species of different classes of molluscs. Preliminary data on Karwar and Konkan coast molluscs were given (paul, 1952-54; Joshi 1969). Molluscs of the Cochin harbour area were studied by Cheriyan (1964, 1968) and Desai (1971). Our knowledge on the opisthobranch fauna of Gulf of Kutch is largely due to Narayan (1968, 1981, 1974) and Burn (1970). Molluscs of Arabian Sea in general were studied by Melvill and his associates between the years 1893 and 1905.

On the east coast, molluscs of the Madras coast have received greater attention. A large number of papers have been published on molluscs in general or with reference to some important molluscs of the Madras coast, Tuticorin, Krusadai Islands and Gulf of Mannar. Many of the earlier reference on the molluscs of the area can be found in Satyamurti (1952, 1954). After fifties several papers have appeared, which presented specific problems, like physiology of a particular species, fishery of certain species etc. There are however, some recent comprehensive accounts on molluscs of Coromandal coast (Rajagopal and Mukherjee, 1982; Mukherjee, 1985) and Cephalopods of Madras coast (Jothinayagam, 1987).

Insular ecosystem of Andaman and Nicobar Islands and Lakashdweep Archipelago is not thoroughly explored. We have only a few desultory account on molluscs of inland and offshore areas of these islands. Although not very exhaustive, a recent contribution on molluscs of Lalcshadweep Archipelago by Surya Rao and Subba Rao (in press) is an attempt at up-datiog our knowledge.

We have several estuaries in our Indian territory. No estuary has been thoroughly explored for its malacofauna, since majority of the papers published deal with only a part of the fauna or with ecology. A satisfactory, to some extent a thorough survey of the Hooghly-Matlah estuary, including Sunderbans, has been conducted by the Zoological Survey of India and the results are being analysed for publication. Some idea of the malacofauna of Mahanadi estuary, Vellar estuary (including Pitchavaram mangroove), and mangroves of Andaman and Nicobar Islands can be drawn from recent works by Subba Rao (1968), Subba Rao and Mukherjee (1974) for Mahanadi; Kasinathan &Shanmugam (1985) for Vellar estuary, Das and Dev Roy (1989) for mangroves of Andamans; molluscs of Krishna estuary, Murty &Rao, 1977). A catalogue with bibliography of estuarine molluscs has been prepared by Subba Rao and Surya Rao (1985).

In general macromolluscan fauna of the easily accessible habitats and ecosystems have been studied. So far Parasitic and pelagic molluscs have received less attention. The latter have been investigated by a few workers such a Sakthivel (1972, 1976). Some studies on interstitial molluscs were conducted by Rao and Ganapati (1968), Salvini-Plawen &Rao (1973). But there is still scope to explore molluscs of deep seas and offshore waters of our seas. We do not have comprehensive data on molluscs of Andaman and Nicobar Islands and molluscs of mainland coastS. Our knowledge of the molluscs of different states is far from complete. We have documents on malacofauna of Manipur (Annandale et al, 1922), Rajasthan (Ray &Mukherjee, 1965), Orissa (Subba Rao et ai, 1989, and in press), Kashmir (Rajagopal &Subba Rao, 1968, 1971), Pune (Tonapi & Mulherkar 1963; Tonapi, 1973; Subba Rao and Mitra, 1975), Himachal Pradesh and Madhya Pradesh (Agrawal 1977, 1978) and Lakshadweep (Surya Rao &Subba Rao, in press). Malacologists in the Zoological Survey of India are currently engaged in the study of molluscs of West Bengal, Tripura, Meghalaya and up-dating of the fauna of Chilka and Hooghly-Mada estuary. ==Estimation Of Taxa Out of the seven recognised classes of Mollusca only five major classes, namely Polyplacophora, Gastropoda, Scaphopoda, Bivalvia and Cephalopoda are represented in the Indian region. Against an estimated total of about 415 families in the phylum, about 257 families presumably occur in the Indian subcontinent and its territorial waters. The National Zoological collections in the Zoological Survey of India comprises of 255 families and a total of about 11,000 species collected from different localities, not only in India but also from other parts of the" world.

Out knowledge of the Indian molluscs is far from complete and hence an accurate assessment of the fauna is bound to be a difficult proposition. However, molluscs of land and freshwater ecosystems have been more thoroughly inventorised than their counterparts in the seas around India. As such the estimation of number of families, genera and species of land and freshwater molluscs is reasonably accurate. But with regard to marine molluscs it is only an assumption based on inferences dmwn from the available collections and literature.

The family-wise break up of molluscs of India and adjacent countries is as given below": Class No. of families Marine Freshwater Land Total

Total 220 21 25 266 Land molluscs

These include both operculate and non-operculate prosobranch and pulmonate snails and slugs. Winckworth (1950) estimated a total of about 133 genera and approximately 4000 species of operculate land snails of the world. In India and adjacent countries there are 525 species of ~d operculates falling into 32 genera. Of the total estimated 667 genera and 15,000 species of pulmonate land snails and slugs, India shares about 104 genera with 950 species. Classified estimates of different categories are given in the following table. The land opcrculates of India include a number of zoogeographically significant genem such as Cyclophorus, Dip 10mmatina and Alycaeus (Order: Mesogastropoda), which have a number of endemic species. Major part of the operculate genera are distributed in South India and Sri Lanka. Subclass Order Families Genera Species

Total 25 137 1487 The family Ariophantidae (order Stylommatophora) is represented by the genera like Macrochlamyst Sitalat Kaliellat Ariophantat Girasiat Austeniat Sesara, Sophina and Durgella which are endemics of Indian subcontinent. Glessula, which shows maximum specialisation among Indian land molluscs is abundant in India but has only a few species in the rest of the oriental region. Boysia (Family Vertiginidae), Lithotes, and Camptonyx (Family Succineidae) are endemic to India; the last mentioned is restricted to Kathiawar in Gujarat. Hyalimax is common to the Andaman and Nicobar Islands and Mascarene Islands. A unique example of land mollusc is Hemiplecta basileus (Ariophantidae), the imperial snail of India, which is endemic to the teak forests in Western Ghats. It is the largest snail, which however, is surpassed by the introduced giant African snail, Achatinafulica. Among slugs, Mariaella and Andenus occur at higher elevations, the former an endemic of Western Ghats and the latter extending upto an altitude of 4000 m. in the Himalayas. Freshwater molluscs Out of 8,765 fr freshwater species estimated to exist.in the world 284 species (56 genera) are reported from India and adjacent countries. According to Subba Rao (1989) the following is the break-up of various categories of freshwater molluscs: The number of freshwater species (India &Adjacent Countries) Class Ordez Families genera species

Total 23 56 284 Among freshwater molluscs there are endemic genera such as Cremnoconchus, a freshwater littorinid occurring in Western Ghats and Mainwaringia, of family Thiaridae, distributed in the Ganges delta. Mysorella distributed in South India, is another endemic genus. Paludomus. FOSSQTulus and Tricula are other important genera. Among gastropods, families such as Neritidae, Assimineidae and Littorinidae are although . marine have a few representatives in freshwater also. Certain families of bivales have contributed

single genus or species to freshwater fauna eg. Scaphula (Arcidae), Novaculina (Solenidae) Taliysiphon (Glauconomidae) and Modiolus (Mytilidae), all living in the Ganges. Indian bivalve fauna is remarkable in that it has two families, namely Unionidae and Pisidiidae of great antiquity and also a family of recent origin, Aetheriidae. The last mentioned family has a discontinuous distribution as it occurs in South America, tropical Africa, Madagascar and India. Marine molluscs Although numerically abundant as individuals and species, marine molluscs have not received the attention they deserve. Several papers have appeared on the marine molluscs, but not sufficient to present a comprehensive data. For some of the families, especially of micromolluscs, there is no basic data of their, occurrence in India seas, or the number of species but are included in the estimate since the territory falls within the known ranges of their distribution. A rough estimate of families, genera and species is as given below. Estimated numbers of marine molluscs of India Class Family Genera Species

Total 220 591 3271 Classified Treatment Class Polyplacophora Systematics' and distribution of Indian ocean chi tons were discussed by Winckworth (1927, 1933) and Leloup (1936, 1937, 1939, 1940, 1952). Recently Rajagopal and Subba Rao (1971) reported 12 species under 7 genera from Andaman and Nicobar Islands. Kaas (1954) reported chitons from Karachi and Arabian Sea. Nagabhushanam and Murti (1968) studied the physiology of reproduction in Chiton granoradiatus Leloup. Kaas and Van Belle (1984, 1985) have brought out two modem and .up-to-date comprehensive monographs out of the total proposed ten-volume series of living chi tons of the world. Class Gastropoda Subclass Prosobranchia Order Archaeogastropoda The order includes a total of about 18 families, but representatives of 11 .families are only reported from Indian waters. Most of the families are marine and only two families have been studied in India. Physiological and ecological studies and structural variations in the shell in relation to distribution of the limpet, Cellana radiata on the Waltair coast were dealt (Balaparameswara Rao and Ganapati, 1979, 1971). Systematics, ecology and distribution gf Patellidae in the Indo-Pacific region were treated in a monograph (powell, 1973).

The ecology, systematics and distribution of Indian neritids were exhaustively treated (Subba Rao, 1975). The chromosomes and biology of some Indian species were investigated (Natarajan, 1969, Govindan and Natarajan 1974} thus laying the foundation for an understanding of the evolution of the group. GrUneberg (1976) investigated the polymorphism in Clilhon oualaniensis. Two economically important families are Trochidae and Turbiridae. Their species composition and distribution have not been iny.estigated. However, investigations were carried out on fisheries of Trochus niloticus and Turbo inarmoratus (Rao, 1939). Although recent surveys were conducted for Trochus and Turbo fishery Rao's work is the only source on reproduction and growth of Trochus. . Order ~esogastropoda About 70 families are recognised in the.order, of which 45 families are reported from Indian territory. Mostly marine, but a few freshwater and land forms are also known. Our knowledge of land operculates, namely families Cyclophoridae and Pomatiasidae, is largely due to Godwin-Austen, Benson, W. H. Blanford, Pfeifer and Beddome. The two families have been exhaustively treated in the Fauna of British India TIl (Gude, 1921). Recent studies were focussed on the chromosomes and biology of four species of Theobaldius occurring in the Western Ghats (Kasinathan and Natarajan, 1968).

Freshwater molluscs constitute nine families and all have been investigated with respect to one aspect or other. Data on various aspects of these studies can be obtained in a recent handbook (Subba Rao, 1989). Three of the families, namely Viviparidae, Pilidae and Thiaridae have attracted more attention than others. There were investigations on the distribution, evolution and palaeogeogrphy of recent and fossil viviparidae. The external ornamentation, evolution of shell sculpture and mantle weIe were also thoroughly studied. The anatomy, including comparative anatomy, ecology and growth rate have also been investigated. Chromosomes and elaboration of enzymes in digestive gland are some other subjects, which have been pursued by Indian malacologists. The family, Pilidae, which include apple snails, is another common freshwater family. In fact, Pi/a can be called as the darling of Indian malacologists since it attracted a number of investigators especially physiologists. After• the publication of Indian Zoological Memoirs of Pi/a (prashad, 1932) a number investigations were carried out on the physiology embryology, ecology and the important phenomenon of aestivation, references to which can be obtained from the Handbook (Subba Rao, 1989).

At the family level the generic limits in Pilidae have been classified by Michelson (1961). The family Thiaridae. which includes maximum number of species among mesogastropods has received considerable attention. The relationships of old and new world melanians have been discussed by Morrison (1954). The family is yet to be revised as far as its systematics are concerned. Ray (1947, 1951) enumerated a few species from Andaman and Nicobar Islands and described a new species from Coromondle coast which however turned out to be an already known one (Subba Rao, 1989). Biology and physiology of some common species have received maximum attention. Seshaiya (1929, 1934, 1935, 1936) investigated the stoin~ch and the anatomy of Paludomus tanschaurica, Melanoides crenulala (Thiara torulosa) and comparative anatomy of melaniids. Physiology of digestion, brood pouch, embryology and development were also subjects of investigations. Latest contributions on the group include those of Muley (1975-1978) and Muley and Nagabhushanam, (1975, 1977). For further information one may refer to Handbook (Subba Rao, 1989).

One often finds in literature the family name Hydrobiidae, which however is not represented in India. All those genera formerly included in that family are now grouped under three separate families, namely Pomatiopsidae, Iravadiidae and Bithyniidae. The family Pomatiopsidae is represented by one subfamily namely Triculinae in India. Davis (1960-1980) made important contributions to our knowledge on the family. The only recent study on the Indian species of •Tricula is by Davis et al., (1987). The information on the families, Iravadiidae, Bithyniidae and also Stenothyridae is old and is available in publications dating back to the first quarter of this century (See Subba Rao, 1989). The famlly Assimir:eidae is common in Indian estuaries but not studied recently by any worker.

Abbott (1958) while dealing with the gastropod genus Assiminea in the Philippines, added useful catalogue of names connected with Assiminea. Except the above discussed few families all other families include marine forms and as far as India is concerned these families were treated in casual and isolated reports. Excellent monographs were published on the families like Littorinidae (Rosewater, 1970), Strombidae (Abbott 1960, 1961, 1967), Cassididae (Abbott, 1968) and Cerithiidae (Houbrick, 1978, 1985) of the Indo¬Pacific region. Anatomy, reproductiv~ biology and phylogeny of the family Planaxidae have been investigated (Houbrick, 1987). The family Cypraeidae has also been ~ell-studied in the Indo¬Pacific region. But most of these studies have not taken into account the collections from Indian seas. Systematics and distribution of Strombidae in the Indian seas have been discussed (Subba Rao, 1971, 1977). Ray (1949, 1951) published notes on cowries. The genus Janthina of the Indian ocean was treated by Laursen (1953) and Ganapati and Subba Rao, (1959).

Pelagic molluscs belonging to the families Atlantidae, Carinariidae and Ptrotrachaeidae have received some attention. Fraver (1869) was perhaps the first to draw the attention to pelagic molluscs. Except for Tesch's works (1906, 1910, 1949) dealing with col1cction~ of Siboga and Dana expeditions there are no recent works on Heteropoda. Benson (1835) described two new species of Carinaria from the Indian ocean. Ramanujam (1945) recorded Re"cluzia• from Bay of Bengal. Sebastian (1963) recorded Cardiapoda placenta in the Arabian Sea. Panikar and Tampi (1949), Natarjan (1957) and Desai (1962) studied egg masses of certain molluscs. The only work which refers to some parasitic molluscs from the Indian seas was by Koehler &Yaney (1908).

Order Neogastropoda The order includes 18 families, which ,are exch}sively marine. The families Tunidae (powell, 1964, 1967, 1969), Vasidae (Abbott, 1969), Thaisidae (Emerson and Cernohorsky, 1973), Harpidae (Rehder, 1973) and Mitridae (Cernohorsky, 1976) were monographed in Indo-Pacific Mollusca. Indian mitres were monographed by Ray (1955) and Subba Rao and Dey (1984). Kohn (1967) Kohn and Robertson (1966) published ecological notes on the cones of Trinc om alee region, Sri Lanka and systematic list of cones of Maldive and Chagos Archipelagoes. U~to-date data on cones of India are provided in two recent pap~rs (Kohn, 1976; Subba Rao, 1980).

Muricidae is a large family and several papers have appeared on it. The Muricidae of the world has been reviewed by Radwin &D'Attilio (1976), who have made important contributions to the knowledge of the family. Breeding habits of som~ common Indian species were observed by Natarajan (1957) and Chari (1968). Subba Rao and Surya Rao (study completed) have thoroughly revised muricids of Indian seas. Nassariidae of Indo-Pacific region has been thoroughly reviewed by Cemohorsky (1980). Subclass Opisthobranchia Order Cephalaspidea The order includes about 15 families of which 9 are'represented in Indian waters. Except for a few references in general faunistic accounts no significant investigations were carried out with special reference to these families. Order Anaspidea (or Aplysiacca) The family Aplysiidae, which has a wide distribution in the Indian Ocean is represented in Indian Seas also. The faniily and its species have been reviewed by Eales (1944, 1960). Bhargava (1968) studied the heart in Ap/ysiaJimbriata. The family is of considerable significance as some of the species have biomedical potentials, which are currently being investigated by NIO and CDRI.

Order Pyramidellacea Semiparasitic molluscs belonging to this order did not receive much attention. Order Acochlidiacea Members of this order are minute interestitial molluscs. Out of the three recognised families two, namely Hedylopsidae and Microhedylidae are known from India. The former is represented by a single species while the latter by two species belonging to two different genera (Rao &Ganapati, 1968). Order Rhodopacea It includes a single monotypic genus Rhodope a ve~iform interstitial gastropod. The only available report did not establish the identify of species (Rao&Ganapati, 1968). Ordez Notaspidea Of the two families Umbraculidae and Pleurobranchidae, the latter only has been dealt, along with other molluscs. A limited number of species were reported by Satyamurti (1952) and Narayanan (1968).

Order Sacoglossa or Ascoglossa

It includes sap sucking sea slugs recognised into seven families of which five families, namely Oxynoidae, Polybranchidae, Stiligeridae, Elysiidae and Juliidae have been hitherto reported from India seas. Excepting the frrst family a few reports have appeared on other families. A few species of Polybranchidae were reported by 0'Donoghu~(1932). Virabhadra Rao (1937) reported a new species of Stiliger (family Stiligeridae) and gave a description of its structure, habits and early development. Virabhadra Rao and Prabhakara Rao (1963) described another new species from the Gulf of Mannar. A few species of EIysiidae were recorded by Satyamurti (1952) and Narayanan (1968).

Bivalved gastropods of the family Juliidae have been adequately covered. These gastropods were reported from the Gulf of Mannar (Prabhakara Rao 1965), Vishakhaptnam and Andaman Islands. Bivalved gastropods of the Indian seas were reviewed by Ganapati and Sarma (1975) and later Sanna (1976) described three new species from eastern Indian Ocean. Order Thecosomata and Gymnosomata Members of these two orders were earlier known under the familiar name Pteropoda. A considerable amount of work was done by earlier malacologists on the group as a whole. Frayer (1869) reported on a collection of pteropods from Bay of Bengal. Stubbings (1938) and Frontier (1963) worked out the material collected dwing different expeditions in the Indian Ocean. The most recent work, on euthoecosomate pteropods which makes a comprehensive coverage of the Indian Ocean is by Sakthivel (1972, 1973, 1976), Sakthivel and Aravindakshan. (1971).and Sakthivel and Haridas (1975).

Ordex Nudibmnchia

The order includes about 47 families, of which about 15 are known from Indian seas. Our knowledge ofnudibranchs with special reference to India is very meagre and scanty. However, there are several references, starting from Alder and Hancock (1866, 1884-85) who laid a good foundation of the subject. Later workers have dealt with a selected number of species of a particular locality. Farren (1905), Eliot (1906, 1909, 1910, 1961), O'Donoghue (1931, 1932), Eales (1938, 1944), Virabhadra Rao (1936, 1952, 1961), Virabhadra Rao and Alagarswami (1960), Narayanan (1968) and Prabhakar Rao (1968) have investigated a few of the Dudibranchs, which however is insufficient to present comprehensive understanding of the group.

Order Onchidiacea The order includes a single family Oncliidiidae, which hitherto was placed under the subclaSs Pulmonata. Fretter (1943) showed its relation to opisthobranchs and a separate order was created to accommodate this family. Stoliczka (1969) gave an account of the species occurring in Lower Bengal, while Prashad (19'30) described two new species of the genus Peronina. A monograph was published on the common species of Onchidium lIe"uculatum by Awati and Karandikar (1948).

Subclass Pulmonata

The classification of Pulmonata by Franc (1968), which was adopted by Runham and Hunter (1970) recognises three orders, namely Basommatophora, Systellommatophora and Stylommatophora. All the three orders are represented in India. Order Basommatophom The order includes 14 families and of these, only six are reported from India. Three of these, namely Ellobiidae, Amphibolidae and' Siphonariidae are marine. Except for occasional inclusion of these families in faunal lists no intensive studies were carried out on these families in India.

Freshwater families, namely Lymnaeidae, Planorbidae and Ancylidae have received co~iderable attention and a large literature is available on the flI'St two. Their systematics, biology of common species, physiology and anatomy have been studied (For details ~Subba Rao, 1989). Order Stylommatophora It is the largest order comprising 58 families and several doubtful ones (Taylor and Sohl, 1962). It includes all terrestrial snails and slugs. The Indian land molluscs fall under about 20 families. Systematics ecology and anatomical detai~ of a few species are dealt with in the Fauna volumes (Blanford and Godwin Austen, 1908; Gude, 1914; Godwin Austen, 1921).

Indian succineids were revised and the anatomy and ecology of some species were studied (Rao, 1924, 1925). Recently Patterson (1970) studied the chromosomes and described new genera and species from India. Ghosh (1958, 1959, 1963) made important contributions to our knowledge on the biology, development, mating and oviposition in Achatina Jurica and a' few other land snails. Breeding, feeding and growth rate in the common garden snail, Opeas gracile were studied•recently (Biswas et al1976; Milra et al1976; Subba Rao et ai, 1981). Growth rate in Gles sula gemma. a c<?mmon land snail in West Bengal has been studied (Subba Rao et al., 1984). Pestiferous nature of some ariophantid snails was explored (Subba Rao 1975) and later pestiferous snails of India are dealt in a more comprehensive manner (Raut and Ghosh, 1984). Ecology of Ariophanla maderaspalana and biology of Ariophanla solala were studied (Masurekar and Bagalkote, 1976; Bhat and Viswanathan, 1972). Most interesting and valuable study of land molluscs is the development of a technique, for farming of the Giant African snail, Achatina fulica, by the Scientists of the Central Inland Capture Fisheries Research Institute, Barrackpore (Vinci et al., 1988). Order Systellommatophora

The order includes garden slugs which cause damage to vegetable crops (Rao and 'Ramdoss, 1953). The common and widely distributed species Laevicaulis alte, has attracted a number of investigators. Its reproductive biology, ecology, food preference, growth rate, fecundity and egg-nesting behaviour were highlighted (Nagabhushanam and Kulkarni, and Nagabhushanam, 1974; Subba Rao et ai, 1989; Raut and Panigrahi, 1988).

Class Scaphopoda

The representatives of the class are exclusively marine and burrow'into sand extending from littoral to deep sea zones. Obviously the collection of these forms needs special techniques and there are not many references on Indian scaphopods, Some information on certain species can however, be obtained from collections made by International expeditions. Scaphopoda collected by the John Murray Expedition, 1933-34 in the Western Indian Ocean was reported by Ludbrook (1954). On the basis of dead shells washed ashore twelve species from Madras beach were reported (Gravely, 1941; Satyam urti , 1956). Eight species were recorded from• the Kerala' coast (Kurian, 1948; Cberiyan, 1968). The only Indian work on the biology of this group deals with the feeding and burrowing mechanisms (Dinamani, 1964).

Class Bivalvia

The classification given .by Newell (1968) in Moore's Treatise on Invertebrate Palaeontology is generally accepted. He recognised 10 orders and about 102 families. Of the latter, about 75 families are represented in India. There had been very few attempts to revise individual families of bivalves in India. Information on bivalves is scattered and is found only in general faunistic works. Prior to 1900, bivalves were dealt in some papers by Melvill and his collaborators, E. A. Smith etc. Bivales of Percy Sladen Trust Expedition were reported by Prashad (1923). He (1932) also brought out an excellent monograph on Pelecypoda of Siboga Expedition. Deep sea bivalves of John Murray Expedition were studied by Knudsen (1967). Ray (1952) described some new species from the Indian Ocean. Bivales of Gulf of Mannar and Gulf of Kutch were reported respectively by Satyamurti (1956) and Kundu (1965). Bivalves of •water bodies of Nagpur were studied by Krishnamurti et al (1968). Ecology and culturing of a few species of edible bivalves were studied by Parulekar et al., (1984).

Freshwater Bivalves

Freshwater bivalves of India are classified into eight families and of these, three families, namely Unionidae, Amblemidae and Corbiculidae are common and distributed throughout India. These three and another family Pisidiidae are well studied and systematically well-documented (Prashad 1921-1933). Our knowledge on the freshwater bivalves of India is documented in the Handbook (Subba Rao, 1989). A significant and intcresting finding is the occurrence of pearls in the freshwater mussel, Lamellidens marginalis (Lamarck) (Janaki Ram, 1989; Raut & Biswas, 1989; Subba Rao, 1989). Fish hosts of the glochidium larva of the freshwater mussel have been studied (Raut &Biswas, 1990).

Marine Bivalves

A large number of bivalves inhabit marine ecosystem. A good number of species are edible and are economically important The Indian work is mainly concentrated on forms like edible oysters, pearl oysters, cocklcs, clams, razor shells and ship worms. Prashad (1933) revised the family Nuculidac. Biology and fishery of Anadara qranosa and taxonomy of blood clams were studied (Narasimhan, 1969, 1988). Anadara in Indian and Pacific waters of Australia was reviewed by Gill (1974).

Systematics and distribution of pearl oysters (Family Pteriidae) were discussed by Prashad and Bhadury (1933) and Virabhadra Rao (19068). Growth rate of pearl oyster was recorded by Gokhale et al (1954). Length-weight relationship of pearl oyster (Alagaraja, 1962) and its breeding (Narayanan 1974) were also investigated. Data OIl pearl fisheries has been well documented. Eswarari et al (1950) and Gokhale et at (1960) for Gulf of Kutch; history of pearl fishery of Tamil coast (Arunachalam, 1952); perl fisheries of Tutieorin (Hornell, 1972; Awati, 1928; Chacko, 1956, 1963; Aruldoss, 1956; Devadoss et ai, 195&) and pearl culture in general (Alagarswarni, 1968, 1971). A manual on pearl cul~ure techniquea as brought out by CMFRI (1984).

Nomenclature and biology of some edible oysters (Family Ostreidae) of the genus Crassostrea were studied by Durve (1960, 1961, 1965, 1967) and 'Durve and Bal (1961). Spawning, development, sex changes and seasonal gonadal changes and rate of growth in spat were studied by Virabhadra Rao (1951, 1953, 1954) and Virbhadr Rao and Nayar (1956). Shell characteristics of the spat of Crassostrea madrasensis and Crassostrea, cucullata as indicator of metal pollution and bioconcentration in iron and trace metals in it are some recent studies (Rajendran and Kurian, 1986; Senthilnathan et al., 1986; Unnikrishnan and Nair, 1986).

Environmental impact on the body component indices and boring and fouling organisms of Crassostrea madrasensis are subjects of latest investigations (lbangavelu and Sanjeevaraj, 1988).

The family Mytilidae includes two species of the genus Perna commonly known as green mussel and brown mussel. Techniques have been developed for the culture of these mussels (Qasim et al., 1976). These are also useful in pollution studies. National Seminar on Mussel Watch organised by the School of Marine Science, University of Cochin in 1986 had focussed the attention on mussels as indicators of pollution and bioaccumulation of trace metals and heavy metals. Mussel Farming, Progress and Prospects (CMFRI bulletin 29, 1980) gives an account of important mussel species and details the techniques of their culture.

Veneridae is a large family comprising a number of commercially important molluscs. The taxonomy of the family is up-dated by Fisher-Piette (1970, 1971). Biology, seasonal gonadal changes, spawning and the rate of filtration in Meretrix casta were studied (Abraham, 1953; Durve, 1963, 1964). The effect of insulin on carbohydrate metabolism and neurosecretory cells in M. casta was studied (Kasinathan, 1962, 1967). The chemical composition of adductor muscle in Meretrix meretrix was analysed (Kalyani, 1974). Biology of Katelysia marmorata and growth rate in Katelysia opima were studied respectively by Joshi (1963) and Virabhadra Rao (1951). Growth and' production of Gafrarium peetinatum from West Coast of India were studied (Ansari et al., 1986).

Two common Indian species of the family Donacidae have attracted some investigators. The growth and annual reproductive cycles of Donax cuneatus were studied respectively by Nayar (1955) and Satyanarayana Rao (1967). Some aspects of the biology of Donax /aba on the Mandapam shore were studied (Alagarsunmi, 1966). A systematic account of all the Indian species of the family Donacidae has been published recently (Subba Rao and Dey, 1985). Growth of the bean clam Donax incarnatus was studied by Nair et al (1978).

Marine timber-boring organisms of the families Teredinidae and Pholadidae have attracted more attention than any other group of bivalves. Systematics of Indian teredinids were studied by several workers starting from Erlanson (1936) to Santba Komaran (1989). Teredinid borers of Sunderbans were studied by Roonwal (1966) and Rajagopal (1961, 1964, 1966, 1970). Collections of these borers were made from several estuaries along the east and west CQast: Mahanadi estuary (Subba Rao, 1968), Visakhapamam coast (Ganapati and Nagabhushanam, 1953-1958), Godavary estuary (Ganapati and Lakshmana Rao, 1959), Krishna estuary (Rambabu et al, 1987), Tamilnadu coast (Nair, 1954-1958, 1961-63, 1965), Vellar-Coleroon estuary (Nair and Dharmaraj, 1980), south¬west coast (Erlanson, 1936), Goa (Santhakumaran, 1983) and Andaman &Nicobar Islands (Das &Devroy, 1989). Work on the wood-borers was summed up in a report prepared by the Forest Research Institute (Purushotam and Satyanarayana Rao, 1971) and in a recent annotated bibliography (Santha Kumaran, 1985). The genera Marlesia and Lignopho/as (pholadidae) in the Indo Pa~ific were revised recently (Turner &Santha Komaran, 1989). Class Cephalopoda

Our knowledge of the systematics of.lndian cephalopods is largely due to Goodrich (1896), Hoyle (1904), Massy (1916), Winckworth (1926), Robson (1926, 1924, 1932), Adam (1939), Moses (1948, 1949), Adam &Rees (1966). A recent catalogue of Cephalopods of Indian Ocean by Silas (1968)( up dates our knowledge on the group. Two new • species and two new records of octopods were reported from the south-west coast of India (Oomen, 1966, 1976 &1977). Recently Jothinayagam (1987) reported 27 species from Madras coast.

There is a regular fishery of cephalopods along our coasts. Biology and fishery of the Palk Bay squid, Sepioteuthis arctipinnis Gould were investigate.d (Rao, 1954). Its embryonic development was also studied (Alagarswami, 1966). The squid and cuttle fish resources of India were reviewed recently (Silas et al., 19832). Ten species were recorded from Visakhapatnam coast and the biology of Sepia acweata was studied (Rayudu, 1982).

Current Studies

In Zoological Survey of India systematics and distribution of molluscs of Tripura and Meghalaya are currently under study. These include land and freshwater molluscs. Our knowledge on marine molluscs is far from satisfactory and hence revision of some families has been taken up. Studies on the family Muricidae have been completed. Mytilidae of Indian seas is currently under revision.

Outside ZSI serious malacologial research is carried out in some centres, namely: Marathwada University, Aurangabad, Centre of Advanced Study in Marine Biology, Porto Novo; Nagarjuna University, Guntur and the University of Calcutta. The studies are mostly aimed at biology, toxicology and ecology. Physiological studies are carried out at Venkateswara and Andhra Universities.

Currently molluscs have attracted attention as sources of biomedical compounds .. Several species of molluscs are screened by the scientists in Bose Research Ins~tute, Calcutta; NIO, Goa; CDRI, Lucknow; Andhra University, Waltair and Regional Research Laboratory (CSIR) Bhubaneswar. Shell fishery is the subject of special investigation at CMFRI. Culture of freshwater pearls is being attempted at the Central Institute of Freshwater Aquaculture, Bhubaneswar. The use of molluscs in pollution studies is practised at several centres.

Expertise India

In ZSI

N. V. Subba Rao, K. V. Surya Rao, H. P. Mukherjee, (Marine) D. K. Thakur, S. C. Mitra, Sipra Maitta, S. Barua, R. N. Manna, Anirudha Dey, A. K. Das (Mangroove mollusus), ZSI, Calcutta. H. P. Agarwal (Land &Freshwater) Central Regional Station, ZSI, Jabalpur. Jotbinayagam, Southern Regional Station, ZSI, M,adras 600 028.

Elsewhere

K. Appukuttan, Central Marine Fisheries Research Institute, Cochin, [Shell fISheries &marine molluscs] Balaparameswara Rao, and M. Rambabu, Deptt. of Zoology, Nagarj~University, Nagarjuna Nagar, Guntur.

R. Kasinathan, Centre for Advanced Studies in Marine Biology, Porto Novo, Tamilnadu, [Mangroove and marine molluscs].

R. Naghabhusanam, and U. H. Mane, Deptt. of.Zoology, Marathwada University, Aurangabad 431 004. [physiology, neurosecretion, marine-molluscs, bore and fouIers]. S. K. Raut, Deptt. of Zoology, University of Calcutta, Ballygunge Circular Road, Calcutta 19, [Ecology of land and freshwater molluscs].

L. N. Santhakumaran, Wood-Preservation Centre (Marine) C/o. National Institute of Oceanography Dona Paula, Panaji, Goa, [Wood borers]. ABROAD Abbott, R. Tucker, American Malacologists P. O. Box. 2255, Melbourne Florida 32902-2255 U.S.A. [Mollusca general, taxon zoogeoganat, conservation etc.] Baba, Kikutaro, Deptt. of Biology Kyoiku Dagaku Minaki Kawabori-cho 43 Tonnoji-Ku, OSAKA, Japan. [Opisthobranch gastropods taxon, zoogeog].

K. J. Boss, Deptt. of Mollusks, Museum of Comparative Zoology, Harvard Univeristy, Cambridge, Massachusetts 02138, [Bivalves, Mus. coIl. taxon, zoogeog. eco1.] J~ B. Burch, Museum &Dept. of Zoology, University of Michigan, Ann Arbor Michigan 481Q4, U.S.A. [Land and freshw. mdl. AnaL, ecol. genetics, Mus. coll. taxon, zoogeog]. Burn, Roben Deptt. of Mollusks National Museum of Victoria Russell Street, Melbourne CI Victoria, Australia, [Opisthobranchia taxon; zoogeog]. W. O. Cernohorsky, Auckland Institute and Museum Auckaldn, New Zealand. [Marine molluscs, Anat. behave ecol., embryol., devel., taxon., zoogeog].

0'Attilio, Anthony Natural History Museum, P. B. No. 1390, San Giego California 92112, [Marine gastropods esp. Muricidae and allied families taxon, ~oogeog, anat., etc.] G. M. Davis, Chairman & Dept. of Malacology Academy of Natural Sciences PhiIa~lphia, U.S.A. Freshwater molluscs especial gastropods. [Taxon., anat., ecol. zoogeog. (Fam. Hydrobiidae, Stenothyridae, Pomatiopsidae etc.)] Gossliner, Terrace Curator of Molluscs California Academy of Sciences San Francisco. [Opisthobranchs; Classification ecoI., taxon., zoogeog].

Henk. H. Dijkstta, Institue voor Taxonomische Zoologie Zoologische-Museum P. B. 4766¬1009 AT Amsterdam, [Netherlands, Bivalves, esp. Fam. Pactinidae &. Propeamussiidae]. Horlcoshi, Masuki, Ocean Research Institute University of Tokyo Minamidel I-IS, Nakano¬Ku Tokyo, [Cephalopods].

Ino, Takashi Nakai (Inland Sea) Regional Fisheries Research Laboratory National Institute of Fisheries Agency 1328 Ujina, Hiroshima, Japan, [Gastropoda embryol., ceol. of Haliotidae] •. R. N. Kilburn, National Museum Pietermaritzburg, South Africa. [Marine molluscs esp. gastropods, taxon, ecol., classification, anaL, zoogeog]. Knudsen, Jorge, Dept .. of Mollusk, Zoological Museum, University of Copenhagen. Universitet sparken 15, Copenhagen Denmark [Mollusca: deep sea forms ecole mus coli taxon' zoogeog]. Allan J. Kohn, Dept. of Zoology, University of Washington, Seatle. Washington 9810S. [Gastropoda esp conidae cool. mus coil. biology, zoogeog]. B. Morton, Dept. of Zoology, University of Hong Kong, Hongkong [Bivalve molluscs especially marine and estuarine].

W. F. Ponder, Western Australian Museum, [Micromolluscs]. Shirley Slack-Smith, Dept. of Mollusca, Western Australian Museum, Francis Street, Perth W.A. 6000 [Australia: oysters (Ostreidae) of the Indo Pacific region]. Sleurs Willy Institute Royal Des Sciences, Naturelle De Belgique, Rue Vautier 29 B-I040, Bruxelles, Belgium, [Gastropoda esp. Rissoidae].

Waren, Anders, Swedish Museum of Natural History, Box 50007, S-10405, Stockholm, Sweden [Marine molluscs Parasitic Eulimidae and others]. Yutaka, Natsukari Associate Professor Laboratory of Marine Zoology Faculty of Fisheries Nagasaki University 1-14, Bunkyo--Machi Nagasaki 825, Japan. [Cephalopods-taxOD, fISheries].

Selected References

Abbott, R. T. & Dance, S. P. 1982. Compendium of Sea shells. A colour guide to more than 4200 of the World's marine shells. 411 pp.

Blanford, W. T. &Godwin-Austen, H. H. 1908. Fauna Brit. India. Mollusca. Testacellidae and Zonitidae, 306 pp. Text-figs. 1-90.

Boss. K. J. 1982. Mollusca. In: Synopsis and classification of living organisms (00. in-chief. S.

P. Parker) I: 945-116, McGraw-Hill Company. Oude, G. K. 1914. Fauna Brit. India. Mollusca ll. Trochomorphidae-JaneUidae S04pp. Text-figs. 1-164.

Oude, G. K. 1921. Fauna Brit. India. Mollusca III. Land operculates, 373 pp. Text-figs. 1-42.

Preston, H. B . .1915. Fauna Brit. India. Mollusca. Freshwater Gastropoda and Pelecypoda, 244 pp. (contains original descriptions of several species). Satyamurti, S. T. 1952. The Mollusca of Krusadai Island (in the Gulf of Mannar) I. Amphineura and Gastropoda Bull. Madras Govt. Mus.• N. S., Nat. Hist. Sec. 1(2) : 1-257 (Illustrations and descriptions of 259 species).

Satyamurti, S. T. 1956. The Mollusca of Krusadai Island (in the Gulf of Mannar) II. Scaphopoda, Pelecypoda and Cephalopoda. Bull. Madras GOVI. Mus., N. S.• Nat. Hist. Sec. 1(2) pt 7: 1-202 (Illustrations and descriptions of 169 species).

Subba Rao, N. V. 1989. Handbook: Freshwater molluscs of India. xxiii + 290 pp. 642 figs & colour plates) (Includes figures for each species and complete bibliography) Vaught, K. C. 1989. A classification of the Living Mollusca (eds. R. Tucker Abbott and Kenneth J. Boss), xii+195 pp. American Malacologists Int., Florida.