Echiura: India
Contents |
Faunal Diversity in India: Echiura
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 phylum Echiura is a small group of unsegmented, coelomate, bilaterally symmetrical and soft-bodied worms, cylindrical or ovoid in general shape, with mouth anterior and anus posterior, with highly muscular sacs filled with fluid in which long alimentary canal and other organs freely move. The common name "spoon worm" for echiurans is derived from the shape of the contracted proboscis-a muscular, sensory and non-Jt.•tractile organ lying at anterior end of trunk.
Status Of The Taxon
Global and Indian Status
Echiura of the world comprises 127 species under 32 genera and 5 families. Of these only 43 species under 14 genera are on record from the Indian ocean. In this respect number of species of the echiuran fauna of the Indian coast is fairly rich in comparison to that of the Indian Ocean Le., 33 species under 11 genera.
Biological Diversity And Its Special Features
Though it is a small group, a wide range of biological diversity has been observed in this taxon. The phylum has been divided into tWo classes and one of the class is further subdivided into two orders and five families. Altogether five families are there under this taxon. Class Echiurida is distinguished by the presence of innermost circular and oblique layers of muscles, anal vesicles and collateral intestine or siphon while the aforesaid characters are degenerated or absent in the class Sactosomatida.
Distribution
The echiuran distribution along the Indian coast depends upon the habitat in which they live. The habitats range from mud, sand to hard substrate extending from intertidal to great depths of the ocean floor. They are burrowers in sand or mud where they make more or less permanent tunnels, sometimes they live under rocks, mud-filled molluscan shells or rock gallaries. The faunal component so far known has been reported only from the intertidal zone of the mainland and insular region. If littoral and sublittoral zones are properly explored, more number of species may be found. About 20% of echiurans need to be explored. Maximum concentration of the number of species is observed at Gujarat including Gulfs of Cambay and Kutch, Lakshadweep, Andamans and Gulf of Mannar. Mud-dwelling forms are few in numbers and found in Kerala, West Bengal and Orissa.
Endemicity
Endemic species are found as fellows : four species of Ochetostoma, five species of Anelassorhync1ws, and three species of Acanthobonellia. The occurrence of Ellbonellia valida, hitherto known only from Arctic ocean and Ecllillnls echillnls, hitherto known form the Arctic, Pacific and the Atlantic oceans are reported from the Lakshadweep and hence are of great geographical interest. In India this phylum is represented by eleven genera, out of them Aclmetobone/lia, Eubone/lia and Rubricelatlls are monotypic.
Value
The Echiura is still regarded as of great scientific and academic interest. Some species are being used in scientific experiments as well as in biological studies.
Threats
The main threat to this taxon is the destruction of habitats. Out of 33 species, five species are mud-burrowers, nine species are sand-burrowers and the rest inhabit under rocks, stones, coral boulders and inside the coral or rock-erevices. Echiurans are reported from the estuarine bodies of India. None of the echiuran species has yet been identified as a keystone species or reported as threatened species.
Conservation
Presently, certain measures have been taken to prevent the habitat destruction. Areas of the Gulf of Mannar and Kutch have been declared as Marine National Parks by the Government. Andaman and Nicobar administration and Lakshadweep administration may also take similar steps so that removal of the natural wealth can be checked.
Selective References
Dattagupta, A. K. 1967. The genera of BonelIidae. Symposium volume on Newer Trends in Taxonomy. Bull natn. Inst. Sci., 34 : 365-370. Dallagupta, A. K. 1976a. Classification above the generic level in Echiurans. Proc. intemat. symp. Biology of Sipuncula and Eelliura, Kotov, 2 : 111-118. Dattagupta, A. K. 1976b. Echiuran taxonomy: The problem of basic number of several variables. Symposium on Modern Trends of Zoological Researches in India, p.68. Dattagupta, A. K. and Menon, P. K. B., 1963. Echiurids from Indian waters with description of two new speices. Ann. Mag. nat. Hist., Ser. 13, 6 : 57-63.
Dattagupta, A. K. and Menoa, P. K. B., 1965. Additions to Indian echiurid fauna. Ann. Mag. nat. Hist., Ser. 13, 8 : 193-200. Dattagupta, A. K. and Menon, P. K. B., 1971. Anatomical notes on four species of Oelzetostoma L. & R. (Echiura) together with a list of the species of the genus. Rec. zool. SUTV. India, 65 : 175-182.
Dattagupta, A. K., Menon, P. K. B. and Johnson, P. 1964. Report on the bonellids collected from the Gulf of Kutch and Port Blair (Ann. Mag. nat. Hist., Ser. 13, 7 : 49-57. Haldar, B. P. 1978. Notes on some Echiura from the east coast of India. Bull. zoo/. SUTV. India, 1 (3) : 315-326.
Haldar, B. P. 1995a, b. Echiura and Sipuncula. Zool. SUTV. India, Wetland Ecosystem Series, Part 1: Funa of Chillea Lake: 479-476; Esturaine Ecosystem Series, Part 2: Hugli-Matla Estuary: 31-39. Haldar, B. P. and Dattagupta, A. K., 1991. Echiura. In : State FOlino Series 2: Fauna of Lakshadweep : 185-197.
Echiura
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Introduction
The Echiura popularly called as 'spoon-worm' are inhabitants of the shores of polar, temperate and tropical seas. They have also been collected from the floor of oceans at great depths.
The rust echiurans described appear to be Thalassema (=Lumbricus) thalassemum (pallas, 1766) and Echiurus (=Lumbricus) echiurus (Pallas, 1766) where the fU'St described bonellid is Bonellia viridis Rolando, 1821. Sedgwick (1898) raised the Sipunculoidea and Priapuloidea to the rank of the phyla but continued to consider the Echiuroidea as a class of tbe Annelida. The Echiuroidea was established as a phylum largely as a result of embryological and developmental studies of Newby (1940) who showed that the echiurans and annelids differ considerably in their mode of development and they are not more closely related to annelids than they are to molluscs. The phyletic status of the group is now generally accepted (Hyman. 1940; Fisher, 1946; Stephen, 1965; Stephen and Edmonds, 1972) and common name i$ echiurans but echiurid for the members of Echiuridae and bonellid for the Bonellidae.
Echiura comprise unsegmented, coelomagte, 1;>ilaterally symmetrical and soft-bodied invertebrates. They are cigar or sausage-shaped creatures, with highly muscular sacs filled with fluid in which the long alimentarycanal and other organs freely move. The name 'spoon-worms' is derived from the shape of the contracted proboscis which is muscular, sensory and lies at the anterior end of trunk but cannot be retracted within the body. The mouth is anteriorby place usually at the base of long proboscis used for gathering food and the anus at the posterior extremity of trunk. A pair of setae are usually present on the ventral surface of the body just posterior to mouth and one or two rings of anal setae encircle the posterior region of two genera. One to numerous nephridia, usually present in pairs, are attached to the ventral surface of the body wall. A part of anal vesicles serves as excretory organ. The sexes are separate, fertilisation is usually external and the larve is a trochophore.
According to Dauagupta (1975) the phylum has been divided into two classes. One of the classes is further subdivided into two Orders and five families as follows: Class Order Family
Sactosomatida In Echiurida body wall consists of innermost circular and oblique layers of muscles; anal vesicles, collateral intestine or siphon, proboscis and anterior setae are present in nearly all species.
In Sactosomatida, proboscis, setae and anal vesicles or siphon are absent and body wall with innermost circular muscles missing or degenerate.
Echiurans inhabit all possible habitats starting from intertidal to the abyssal region of the ocean. Bonellids have been dredged from depths of 6,000-10,000 m. Sometimes echiurans are very B. P. Haldar, Zoological Survc:y of India, Calcutta. common in a particular locality. Their size also varies from a few millimeters to 25 centimeters in length. As they are soft-bodied and almost defenceless creatures they always live in protected places and are well adapted for living in burrows. They are found in sand or mud where they sometimes live in U-shaped burrow, under rocks, in debris, amongst root of marine angiosperms, in the discarded shells of echinoids and in cracks and galleries in rocks. Echiurans are deteritus feeders. With the aid of their highly muscular and sometimes spoon-or scoop..like proboscis they suck sand, mud, coral fragm~nts and finely divided particles from their surroundings int9 their mouths and extract organic matter from the ingested material. Some species, however, trap bacteria and very fine particles of food in a slime net which is secreted from the swface of the animal.
Historical Resume
The knowledge of echiurans from the Indian coast is meagre. The earlier work were carried out in a rather suay fashion from different coastal belts of India.
The pioneering work on the Indian echiurans dates back to 1903. Echiurans of the Minicoy Island in the Lakshadweep collected during Gardiner's expedition to the Maldive and Laccadive Archipelagoes, were swdied by Shipley (1903) but unfortunately his collection is not traceable in any museum in Great Britain. This was subsequently followed by Annandale and Kemp (1915 ¬fauna of Chilka and Gangetic delta), Annandale (1922 marine element in the Ganges), Prashad (1919-1935), Awati (1936, 1938), Awati and Deshpande (1933-1936) and Awati and Pradhan (1935-1936).
For nearly two decades after Prashad and others (1936) there appeared no publication on this group in India though the work on this group progressed rapidly in other parts of the globe,. Gideon (1951), Gideon et ale (1956), Jose (1964), etc. recorded some echiurans fro!1l the Gulf of Kutch. Menon and Dattagupta (1962, 1964) and Dattagupta and Menon (1961, 1963, 1964, 1965, 1971 and 1975) described and reported several echiurans from the Indian waters., Dattagupta in 1967 de81t with genera of bonellids and in 1915 presented a super in 1974 on Anelassorhynchus, in 1976 on echiuran taxonomy. generic classification in echiurans Mathews (1915) dealt with geographical distribution of Indian echiurans.
Beside the taxonomical aspects, Dauagupta and Surendra Sing (1965) studied histological difference between two closely related bonellids 8I)d in 1975 on morphology and histochemistry of segmental organs of a few echiurans. Other wise on echiurans are by Menon (1975) on coelom and coelomic elements, Menon and Dattagupta (1975) on main vessels and sinuses, Menon and Sareen (1975) on female reproductive system and Mathew (1975) on the integument. Subsequently, Dattagupta and Singhal (1978-1982) published several papers on echiuranbiology and'ecology.
Apart from the Indian forms, Dattagupta studied the deep water echiurans of the world -'vema' collections (1975), Caribbean deep sea bonellids (1977), Atlantic echiurans (1981), Indian Ocean echiurans (1983), Atlantic echiurans (1981), Indian Ocean echiurans (1983), echiurans from Venezuela basin (1991) and benthic community of the Bay of Biscay.
For more then a decade (1978-1991) taxonomic studies in the Zoological Smvey of India have made some progress. Haldar (1978, 1981) studied echiurans from the east coast of India and from the Gulf of Cambay . HaleJar (1985) also studied the ecology of a species from Gujarat coast this recent contribution on this group' is from, the Lakshadweep (in press). Results of studies on estuarine ecosystems of the Hooghly-Matla and Chilka Lagoon have been finalised.
Studies from Different Environs
The habitats of echiurans range from sand, mud to hard substrate extending from intertidal to abyssal depth. They are burrowers in sand or mud, where they fashion more or less permanent tunnels. Sometimes they live under rocks, mud ..Jilled mollusc shells or sand-dollar tests, which afford some protection or the rock g~eries excavated by bOring clams.
Earlier work except those of Annandale & Kemp (1915) & Prashad (1919-1935) contained only casual references to the nature of the habitat Later work contained some information on the general nature of the environment from where the fauna have been collected but mainly related to the intertidal and littoral forms. Dattagupta et at. (1962, 1966) studied taxonomy, ecology and zoogeography of some forms from Gujarat, Gulf of Kutch, Kerala and Andamans. Mathew (1975) studied the geographical distribution of the Indian forms. Haldar (1981) discussed in detail the ecology of an echiuran from the Gulf of Cambay.
Our knowledge of deep sea forms is still poor. Work on the Echiuran biology started at the university level in mid-thirties.Work of Prashad and Awati (1935) on reproductive and segmental organ and Awati and Deshpande (1933) on the development of a species, and burrows, food-getting and respiratory movement of the same species in 1935 (a, b &c) deserve mention. After a gap of two decades Gideon (1957), Gideon et ale (1956) and Jose (1964) while working in Marthawada University made some contribution on echiuran taxonomy of Gulf of Kutch. More or less at the same time Dattagupta and his team at Pilani University started work on echiuran taxonomy (1961¬1971), histology and histochemistry (1963, 1964, 1966), same aspects of echiuran biology (1976a-e, 1982) and echiuran ecology (1979, 1980). Echiuran ecology is also dealt by Haldar (1981, 1985) at the Zoological Swvey of India.
Estuarine ecosystem of this group has attracted still less attention. Earlier work of Annandale &Kemp (1915) reported two species, one each from brackish water near Calcutta and Chilka Lake. Haldar (1985) reported faunal wealth of this group from the Indian estuaries. Recent contributions on this group from estuarine ecosystems of the Hooghly-MatIa and Chilka Lagoon are finalised by Haldar.
Estimation of Taxa
Echiura of the world comprise 127 species in 32 genera under 5 families. Of these, only 43 species under 14 genera are on record from the Indian Ocean., In this respect echiuran fauna from the Indian coast is fairly rich in comparison to that of the Indian ocean.
Out of 20 genera under bonellids each of 11 genera is represented by one species and are exclusively deep water forms of either the Pacific or the Atlantic Ocean. Out of 11 echiuroid genera 6 are inhabitants of the Indian Ocean as well as Indian subcontinent Distribution Pattern of Echiuran Fauna In India Region No. of species
As per the information available from the literature as well as from author's field observations it may be inferred that 33 species are known from the intertidal zone of mainland and insular areas of indian subcontinent. Out of 33, 5 species are mud-burrowers, 9 sand-burrowers and the rest dwell under rocks, stones'; coral boulders and inside the coral or rock crevices. Truly deep water forms are still unknown in the Indian waters. Like sipuncu~s, echiurans too are reported from the estuarine areas of India by Annandale and Kemp (1915) Prashad (1919) and Haldar (1978, 1985).
Classified Treatment
In addition to taxonomic studies some other aspects of echiuran biology are available in the literaturel Awati and Deshpande (1933-1936) and Prashad and Awati (1935) studied the reproductive and segmental organ of Thalassema bombayensis , Awati (1936, 1938) on proboscis and ciliated apparatus of T. bombayensis, Awati and Deshpande (1935-1936) on the food-getting, respiratory movement, alimentary canal of T. bombayensis. Dattagupta et ala (1964) studied the morphology and histology of males of Acanthobonellia, Dattagupta and Singh (1966) on histological difference between two closely related species of Acanthobonellia, Dattagupta and Singh (1976) on morphological and histochemical studies on segmental organs of a few echiurans, Dattagupta and Menon (1976) on main vessals and sinuses in a few species echiurans, Dattagupta and Singhal (1979) on burrowing and feeding behaviour of a few echiurans, in 1980 on ecology of some echiurans, and cytological studies on Achethobonellia maculata, and in 1982 on some aspects of reproduction in Achaetobonellia maculata. Current Studies
In Zoological Survey of India. studies on systematics and distribution of echiurans are at present undertaken with emphasis on state-wise faunal resources. The projects on echiuran fauna of the Chilka lagoon and the Hooghly-Matla estuary have been completed. Elsewhere in India there appears to be no work on this group at present.
Outside India, several scientists, particularly from U.S.A. France, Brazil, U.S.S.R., Australia and Japan are engaged in ecobiological, physiological. histochemical, developmental and evolutionary studies.
Expertise India
In ZSI
B.P. Haldar, Zoological Survey of India 27, JL. Nehru Road, Calcutta -700 016, West Bengal
R.N. Singhal, Department of Zoology, Kurukshetra University, Kurukshetra, Haryana.
Abroad
S.J. Edmonds, Honorary Associate, South Australian Museum, North Terrace, Adelaide South Australi~ 5000
V.V. Murina, Institute of Biology of Southern Seas, Academy of Sciences of Ukranian SSR, Sevastopol, 335000, U.S.S.R. Mary E. Rice, Smithsonian Marine Station at Link Port, Fort Pierce, Horida, Fl 34946,
U.S.A. John F. Pilger, Department of Biology~ Agnes Scott College, Decatur, GA 30030, U.S.A. A.S.F. Ditadi, University of Sao Paulo, Sao Paulo, Brazil.
Selected References
Dattagupta, A.K., 1967. The genera of bonellidae. Symposium Vol., Newer Trends in Taxonomy. Bull. natk. Inst. Sci., 34 : 365-370. Dattagupta, A.K. 1983. Echiurans of the Indian Ocean, south of Madagascar. Bull. Mus. naln. Hist. nat. Paris, 4 sere SA: 1045-1050.
Pilger, J.F. 1978. Settlement and metamorphosis in the Echiura : a review. In: Chia, F.S. & Rice, M.E. (Eds). Settlement and metamorphosis of marine invertebrate larvae. 290 pp. Rice, M.E. & Todorovic, M.{Eds.) 1976. Biology of the Sipuncula and Echiura. Proc. interna.t. Symp. biology of the Sipuncula and Echiura. Vol. 2 : 204 pp.
Shipley, A.B., 1902. Echiuroidea. In : Gardiner, J.S., Fauna and Geography of the Maldive and Laccadive Archipelagoes, 1 : 127-130, p1.6. Stephen, A.C. & Edmonds, S.U., 1972. The Phyla Sipuuncula and Echiura. Trustees of the British Museum (Nat. Hisl), London, 528 pp., 60 figs., 17 tabs.
