Protochordata: India
Contents |
Faunal Diversity in India: Protochordata
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
The term Protochordata is a common name to indicate the fauna which possess cartilaginous notochord either as adults or during their developmental stages of life history and are regarded as forerunners of the chordates. Taxonomically, this includes subphylum Cephalochordata and subphylum Urochordata (=Tunicata), both of which come under phylum Chordata along with subphylum V~rtebrata. This term Cephalochordata implies the meaning of the presence of a notochord throughout the length of the body including the head region. Known otherwise as lancelets, these are exclusively marine organisms resembling a primitive fish, the present day example depicting the phenomenon of evolution of true chordates.
The term Urochordata on the other •hand implies the meaning of the presence of a notochord in the tail region of a group of Protochordates either in the adult form or during the life history stages of the developing larvae. All the organisms of this group are covered by a coat or h.inic which is either leathery or gelatinous, and opaque, translucent or transparent. The subphylum Urochordata (=Tunicata) is divided into class Ascidiacea which are sessile or benthic, class Thaliacea and class Larvacea which are planktonic. The Thaliacea possess the notochord in their larval stages and the Larvacea retain the notochord as adults that helps their locomotion with the tail.
Status Of The Taxon
Global and Indian Status
As mentioned earlier "Protochordata' is a common name that includes two subphyla, viz., Cephalochordata and Urochordata. The Indian position of these taxa in global context is depicted in Table -1. DHANDAPANI: Protochordata Table -1 Showing number of families, genera and species of Protochordata reported from India and world.
Distribution
Cephalochordates have been collected from Chennai city coast, Tuticorin coast and in the atolls of Lakshadweep Islands. While three species of Braclziostoma have been recorded from Chennai city coast, only one species B. belcheri is known from Tuticorin. Epigonycthys cynglllense and E. lllcayanllm were recorded from Tuticorin and Lakshadweep Islands respectively. Ampltioxides occurs commonly in oceanic plankton. Although, a major work was done from the Tamil Nadu coast, ascidians occur all over the coast of India. They are one of the major components of fouling organism found on the bottom surface of ships and boats, pillars and warfs and the outflow openings of any pipeline submerged in the sea.
As planktons the Thaliacea are distributed in all seas. When they occur in swarms they are abundant in the near shore areas and are occasionally driven into the coastal water bodies that are connected to the sea. Being planktonic, the Larvacea are distributed all over the world oceans. Most of them are stenohaline. A few euryhaline species like OikoplclIra dioca has been recorded from the Chilka Lagoon, Orissa recently.
Biological Diversity And Its Special Features
The Cephalochordates are represented by two families, viz., Branchiostomidae and Epigonyethidae. The former is represented by the single genus Branchiostoma and the latter by genus Epigollycthys. The so called genus Amphioxides is presently recognised as a prolonged larval phase of species of the genus Epigonycthys. Three species of Brallc11iostoma and 2 species of Epigonycthys occur in Indian seas. Occasionally AmpllioxlIs is recorded amongst oceanic plankton. Urochordes are represented by 3 classes, viz., Ascidiacea, Thaliacea and Larvacea. The class Ascidacea consists of 2 orders-Enterogona and Pleurogona while class Thaliacea is represented by 3 orders, viz., Salpida, Doliolida and Pyrosomida. The class Larvacea, however, comprises of 2 families-Oikopleuridae and Fritillaridae.
The cephalochordates always occur half burried in coarse sandy floors. They are very quick in their movements and occur in dredged collections "that contain coarse sand. Occasional plankton samples which contain large number of post larval cephalochordates indicate mass breeding phenomena in the population.
The ascidians have the adaptability to settle on any substratum in the marine environment as biofoules. They sometimes look like mats or spongy algae and occur in the form of encrusted layers. The Thaliaceans are pelagic tunicates leading a holoplanktonic life. They are covered by a transparent tunic and exhibit an alternation of generation of sexual and asexual reproduction.
The larvacea evolved as neotenic forms of ascidian tadpole larvae. Their body is enclosed in a chamber which acts more as a feeding chamber. The tail is used for locomotion and to create feeding current.
Endemicity
It is very difficult to assign marine organisms, more particularly the marine planktonic organisms as endemic to any particular area.
Value
The developmental stages of cephalochordate eggs are used in academic circles to teach basic chordate embryology. Branchiostoma belcheri is of fishery value off the south China sea. Thaliacea and Larvacea are indicators of water masses and thereby help in predicting a particular fishery belonging to a particular water mass. Thaliacea are decimators of phytoplankton bloom and maintain a balance between zooplankton and phytoplankton proportion in the sea.
Threats, Conservation Strategies And Future Studies
Presently no species of Cephalochordates and Urochordates is under threat. However, constant discharge of effluents from various industries tend to pollute the intertidal and shelf areas affecting the benthos and their habitats. One among such areas are the sandy substratum which could allow these effluents to percolate, changing the seafloor into unsuitable substratum for cephalochordates. Methodical survey of benthos and seasonal analysis of plankton for cephalochordate and urochordate adults and larvae respectively would reveal the presence of both new taxa and new distributional areas. Enormous scope is also available in the field of taxonomy, biology and biomedical studies of ascidians.
Selected References
Azaria, J. 1965. Studies on the Cephalochordates of the Madras Coast. /. Taxonomic study. J. Mar. Bioi. Ass. India, 7(2) : 348-363. Bigelow, H. B. and Farfante, /. P. 1948. Fishes of the Western North Atlantic Lancelets. Memoires of the Sears Foundation for Marine Research, 1 : 1-28. Dhandapani, P. 1996. Pelagic tunicata from the seas around Andamans and Nicobar Islands. Proc. Second Workshop Scient. Resu/. FOR V Sagar Sampada, pp.217-227. Feneaux, R. 1969. Les Appendicularis du Golfe du Bengale. Mar. Bioi., 2 (3) : 252-263. Gibbs, P. E. and Wickstead, J. H. 1969. On a collection of Acrania (Phylum Chordata) from the Solomon Islands. Journal of Zoology, 158: 133-141. Herdman, W. A. 1910. Ascidians and Amphioxus. The Cambridge Natural History, 7: 112-138. Prashad B. P. 1934. On a collection of Indian cephalochordates with notes on the species from the Indian Museum, Calcutta. Rec. Ind. Mus., 36 : 329. Miller R. H. 1955. On a collection of ascidians from South Africa. Proc. zool. Soc. London., 123(2) : 277-325. Sewells, R. B. S. 1926. The SaIps of the India Seas. Rec. Ind. Mus., 28: 65-126. Thompson, H. 1948. Pelagic Tunicates of Allslralia. CCSIR, Australia, pp. 196, pI. 75. Tokioka, T. 1951-1961. Contribution to the Japanese ascidian fauna. Publ. Seta. Mar. Bioi. Lab. Japan.
Protochordata
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Introduction
Protochordata comprises of two sub-phyla, Cephalochordata and Tunicata. Sub-phylum Cephalochordata has Class Leptochordii. Tunicata has three Classes, viz. Ascidiacea, Thaliacea "and Larvacea. The protochordates are exclusively marine and occupy various niches in the marine ecosystem. The present status of our group in India is as such based on the work done on the Marine Survey Collections made on board R.I.M.S. "Investigator" , the vessels in the Pearl Oyester fisheries, the collections made by the Central Marine Fisheries Research Institute on board the R. V. Varuna, collections made by the various university laboratories of the maritime states and the"collections of the International Indian Ocean Expedition.
Historical Resume
Cephalochordata : Gray (1847), Thurston (1890), Tattersall (1903) and Foster-Cooper (1903) worked on the samples collected from the Indian Seas, including the Laccadive &Maldive Island collections. Prashad (1934) worked on the collections available in the Zoological Survey of India and described four species. Azaria (1963, 1966, 1967), working on the collections made off Madras coast has described three species.
Ascidiacea: Herdman's (1906) description of ascidians from the Gulf ofMannar was the rust on Indian ascidians. Oka (1915), a visiting Japanese Scientist, worked on the deep sea collections made on board R.I.M.S. "Investigator" and described "II new species .belonging to the families Cynthidae, Styelidae, Ascididae and Clavinidae, which included an aberrent. deep sea form, Hexacrobilus indicus. Das (1936-'45) and Sabestian (1942-59) worked on the ascidian fauna of the Madras coast; the former studied Pyuridae while the latter covered the families Polyclinidae, Peraphoridae, Pyuridae and Styelidae. Prakasam (1978) in his short work, added knowledge to the fauna of Madras coast. Ranganathan (1982-1988) has extensively covered various families of ascidians from his collection off southeast coast of India. From the Bombay coast, Karande (1969) noted six species of ascidians acting as foulers in the harbour. Miller (1988) worked on the ascidians brought by the International Indian ocean Expedition team.
Thaliacea: Bomford (1913) initiated the study on salps collected on board R.I.M.S. "Investigator" and this was followed by Sewell (1926) to complete a monograph. Nair &Aiyer (1943) and Nair (1949) recorded sixteen species of pelagic tunicates (salps &doliolids) collected off Madras coast. Ganapatby &Bhavanarayana (1958) gave a list of pelagic tunicates (salps, doliolids and Larvacea) and pointed out their significance as indicators of ocean currents in Bay of Bengal. Sabestian (1968) described a new encrusting species of Pyrosoma from the Arabian Sea. Swarming behaviour of salps were observed by Nagabhushanam (1960) off Andhra coast and by La! Mohan (1965) off Gujarat coast. Dhandapani (in press) presented a paper in the Symposium on Indian ocean and adjacent seas at Cochin, in which he indicated the presence of fourteen species of doliolids (including new taxa) in the Arabian Sea. Dhandapani (1977) described eight species of doliolids including new records from the Bay of Bengal. Van Soest (1981) has published monograph on Pyrosmatida in which he described several new species from Indian Seas.
Larvacea : Fenaux (1974), working on the International Indian ocean Expedition material; has described many species of appendicularians from the Bay of Bengal. Chandrika (1974) recorded a rare appendicularian of the family Kowlevskidae. Dhandapani (1977) described two new species of Larvacea from the Bay of Bengal.
Dhandapani (1977) has worked out the collections made on board the vessels R.I.M.S. "Investigator" ,R.V. "Vityaz" and I~.S. "Kistna" and added two new species of appendicularians, five species of doliolids and one species of Amphioxids •as new to Bay of Bengal. Three species of salps and eighteen species of Larvacea have been added as new to National Zoological Collections. The collections of I.N.S. "Dharshak" and those of F.D.R.V. "Sagar Sampada" are being worked out for Protochordata.
In India, Ranganathan (Hindu College, Tuticorin), Jayapaul Azaria (Zoot. Dept, University of Madras) and Bhavanarayana (Zool. Dept., Andhra University) continue to work on Ascidiacea, Cephalochordata and Salpida respectively.
Scientists outside India are interested on diversified aspects of the subject, i.e. physiology, embryology, cytogenetics, cytochemistry and computer analysis of the population, etc. Monniot (Museum Nationale de Historie Naturalle, Paris), Patricia Kott (Queensland Museum, Australia), Miller (Marine Laboratory, Scotland), Jefferies, (British Museum of Natural History, London), Tokioka (Seto Marine Biological Laboratory) are interested in taxonomy of ascidians. Godeaux (Institute of Van Beneden, Belgitlm), Bracconot (Statione Zoologique, France), and Van Soest (Zoological museum, Amsterdam) are experts in Thaliacea. Feneau, (Station Zoologique, France) is an expert on Larvacea. Tokioka (Seto Marine Biological Laboratory, Japan) is interested in all groups of pelagic tunicates.
Areas to be Explored
Survey : Dredging should be undertaken beyond 100m level all over Indian Ocean and its insular waters. This will help to have more knowledge on benthic fauna of Protochordata.
Taxonomic study: Among sessile tunicates, families Polycitridae, Dideminidae, Diazinidae, Cionidae, Corellidae, Octonimidae. Sortillidae and Molgulidae are to be worked out
Estimation of Taxa
Expertise India
In ZSI
P. Dhandapani -Marine Biological Station, Zoological Survey of India, Madras ¬[Protochordata except ascidians].
Elsewhere
P. V. Bhavanarayana, Dept. of Zoology, Andhra University, Visakhapatnam -3. [Salpida]. Jayapaul Azaria, Dept. ofZoology, University of Madras, Madras -20 [Cephalocbordata].
T. Ranganathan, Dept. of Zoology, Hindu College, Tuticorin, Tamil Nadu -[Ascidiacea].
Abroad
N. J. Berrill, 410, Swathmore Avenue, Swathmore, Pennsylvania, U.S.A. [Tunicata].
J. C. Bracconor, Station Zoologique, Villefranche -sur. Marine, France [Doliolida].
R. Feneaux, Station Zoologique Villefranchesur, Marine, France. [Larvacea].
R. W. M. Van Soest, Institute of Taxonomic Zoologic, University of Amsterdam ¬[Thaliacea].
H. John, Wickstead, The Marine Biological Association, Citadal Hill, Plymouth, England -[Cephalochordata].
