Hemichordata: India
Contents |
Faunal Diversity in India: Hemichordata
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 hemichordates are "more or less enterocoelous coelomates with the body and coelom regionated into three successive divisions of unequal length and different structure" (Hyman, 1959), and are exclusively marine origanisms occurring from the intertidal region to great depths. The term Hemichordata implies the meaning of the presence of a notochord in the middle region of the body but, the embryological evidences prove that the so called notochord is not a true notochord of middorsal origin but is only a buccal diverticulum (Hyman, 1959) developed into a "rachis like" organ presumably to support the function of the proboscis in enteropneust worms than of any use in the other groups of hemichordates:
Status Of The Taxon
Phylum Hemichordata is divided into three classes, i. e., Enteropneusta, Pterobranchia and Planctosphaeroidea. Four families under Enteropneusta are known (Ptychoderidae, Harrimanidae, Spengilidae and Saxipenniidae), of which all but Saxipenniidae have been recorded from India, thus indicating the possibility of finding more taxa in Indian waters. Both Pterobranchia and Planctosphaeroidea have so far not been recorded from Indian waters. The status of the taxon in global and Indian context is depicted in Table -1. Table -1 Number of hemicherdate taxa in the world and India
Distribution
The species of the Enteropneusta occur both in tropical and temperate waters. Genera Ptycllodera, BalanoglosslIs, Glossobalanlls, Glandiceps, Saccogioslis and Ha"imania are popularly known by their occurrence in all the oceans of the world. Pterobranchs are usually colonical forms but live in individual tubes. These are well studied from temperate waters but rarely from tropical belt, the reason could be due to improper coverage of this belt for study. The planktonic Planctosphaeroidea are oceanic in distribution and are rarely collected.
From Indian waters enteropneust worms of the genera Ptychodera, Glossobalanlls, Glandiceps were collected from the Gulf of Mannar, Gulf of Kutch, Andaman Seas, Lakshadweep & Maladive Seas, the Tamil Nadu coast upto Cape Comerin (Zoological Survey of India records), and from the high saline marshy areas of Sunderbans, in West Bengal, the genus Saccoglossus were recorded. The reported occurrence of Saccoglossus from Sunderbans is a new record and indicates that intense search is likely to lead to the discovery of more species in other parts of Indian coastal region. No authentic report on the occurrence of either Pterobranchia or Planctosphaeroidea is available for Indian waters. PtycllOdera j1ava appears to be more endemic to Gulf of Mannar region, although one specimen of colour variety (blackish brown) was recorded from Cape Comerin, Glossobalanus minutus seems to occur more along the coasts of oceanic islands, i.e., Andaman and Lakshadweep groups. The Saccoglossus sp. collected from Sunderbans is a new record and perhaps endemic.
Biological Diversity And Its Special Features
Class Enteropneusta consists of solitary, vermiform burrowing organisms belonging to four families, i.e., Harrimanidae, Ptychoderidae, Spengilidae and Saxipennidae. Since these worms live burried in the seafloor, and as they are also fragile, it is possible that great many species of this group remain uncollected. This evident from the occurrence of tomaria, the larvae of enteropneust worms, of varying descriptions, occurring regularly in the plankton samples collected all over the world which indirectly indicates the rich taxonomic diversity of the group.
Class Pterobranchia consists of tentaculate, solitary or colonial forms, usually tiny or even, microscopic in size. The class includes only three genera, i.e., Cephalodiscus, Atubaria and Rahabdopleura. While genus CephalodisclIs is a well studied group, the genera Atllbaria and Rlzabdoplellra need extensive survey and intensive study. Class Planctosphaeroidea is known by a single species Planctosphaera pelagica. The description reviewed by Hyman (1959) indicates that this group may perhaps be a neotonic from of a Tomaria larva and adopted to planktonic life.
Endemic And Threatened Species
But for Planctosphaera spp., all other species are benthic in habitat. By studying the habit of Ptyc1lOdera flallva, it may even be assumed that some species may be occurring as "locally distributed communities" The only commonly available enteropneust worm in India is Ptyc1lOdera flallva which is extensively used for studies hence faces threat of over exploitation.
Value
Although no economic value can be attributed, there are reports of Ptychodera flauva being used as fish line baits.
Threats
Ptychodera flauva is the only species that is within the easy reach of collection at one point of intertidal region in Krusadai Island of the Gulf of Mannar area and is likely to be over collected for research if proper measures are not taken to prevent it. Rarity and endemism of certain species along the intertidal region of island ecosystems emphasises the need to preserve this taxon.
Conservation Strategies And Future Studies
Presently no action is taken to conserve this group in particular except that intense care is taken to avoid over collection of Ptychodera flauva from the Gulf of Mannar Biosphere Reserve which incidently is also a Marine National Park. Complete ban or moratorium for three years on collection of this species either for research or as demonstration species in educational institutions from the Gulf of Mannar Biosphere Reserve should be imposed in order to establish an appreciable density of population which is expected to encourage settlement of this species in new areas. Intense survey of ocean floors with the use of suitable gears is needed to unravel the mystry of hemichordate diversity not only in the areas around India but also in other parts of the globe.
Selected References
Harmer, S. F. 1910. Hemichordata. The Cambridge Natural History, 7: 3-32. Hyman, L. H. 1959. Phylum Hemiehordata.In : The Invertebrates, 5: 72-207. Me Graw Hill Book Company, New York. Ramunni Menon, K. 1994. Enteropneusta from Madras. Quart. J. micro Sci., 47 : 123¬131, pI. 10. Singh, B. N. and A. Choudhury, 1992. Hemichordata. Fauna of West Bengal; State fauna Series 3: (Rec. Zool. Survey) pt. 2 : 243-438. Spengel, J. W. 1893. Die Enteroprenusten des Golves Von Neape!. Fauna and Flora des Golfes Von Mongr., 18. Thomas, I. M. 1956. Saccoglossus apantesis a new species of enteropneust from south Australia. Trans. Roy. Soc. S. AI/st., 79 : 167-176. Van der Host, C. J. 1939. Hemichordata. In : H. G. Bronn (Ed.) Klassen and Ordungan des Teerreiches, f: abt. Buch 2, Teil 2.
Hemichordata
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Introduction
Phylum Hemichordata consists exclusively of marine organisms occurring from tidal areas to great depths with few planktonic representatives. It is divided into three classes, i.e. Enteropneusta, Pterobranchia and Planctosphaeroidea. Our knowledge on this group in India is based on the collections made from the Gulf of Mannar, Madras coast, Andaman & Nicobar Islands, Laccadive Islands and the Gujarat coast.
Historical Resume
Punnet (1903) described enteropneust worms from Laccadive and Maldive Islands. Menon (1904) working on dredged collections off Madras coast, described three species of which one was new to science. Later, Rao (1955) followed it up to describe several more species from the same area. Ptychodera flava from Krusadai Island was made more popular by other workers (but wrongly identified by few as Balanoglossus) i.e. Rao (1934), Ramanujan (1935), Devanesan &Varadarajan (1940), Kuriyan (1949) and Rao (1953, 19$5 & 1962). Balasubramaniam (1978) described two species of Tomaria from Porto Novo waters. Pillay (1950) described the only enteropneust worm collected fonn Gujarat coast
Pillay (1950) identified specimens of enteropneust worms collected from Okha coast. Glandiceps "w/ayanus and Glossobalanus minutus were identified by Dhandapani from Andaman &Nicobar Islands and Maldive Islands. No samples of either Pterobranchia or Planctosphaeroidea were collected so far by the Zoological Survey of India parties. The Tornaria larvae that were collected during the 46th cruise on board F.O.R. V. Sagar Sampada and those that are being collected by RV Chota Investigator are being worked out by P. Dhandapani at Marine Biological Station, Madras. Further, Dhandapani during his recent surveys of the Gulf of Mannar, discovered the presence of Ptychodera flava (Enteropneusta) both near the Pamban Light House area and the Pullivasal Island.
Jayapaul Azaria, University of Madras conducts bio-chemical experiments on Ptychodera flava. Balasubramaniam, CAS for marine biology, Porto Novo, worked on Tomaria larvae. Bjorn Berg, Universidae de Sao Paulo, Brazil, and Staisny, Institute of Van Beneden, Belgium also work on Tomaria. Burdon-Jones, Plymouth Laboratory, England, and Thomas, University of Adelaide, Australia are experts on enteropneust worms. Practically no work on Pterobranchia is being done anywhere in the world.
Areas to be explored
Survey: Dredging should be done beyond 100 Il) level allover the Indian Ocean and its island waters: efforts should be made to look for hemichordates since this group is not covered adequately from Indian waters.
Taxonomic study
Taxonomic studies on families Protobalanidae, Cephalodiscidae and Planctospaeridae need to be undertaken.
Expertise India
In ZSI
P. Dhandapani, Marine Biological Station, ZSI, 100, Santhome High Road, Madras -28. [Enteropneusta].
Elsewhere
M. Balasubramaniam, Reader, CAS for Marine Biology, Porto Novo, Tamil Nadu, India. [Enteropneusta].
Jayapaul Azaria, Reader, Dept. of Zoology, University of Madras, India. [Enteropneusta].
Abroad
Barrington, E. J. W., Dept. of Zoology, The University of Nottingham, England. [Enteropneusta].
Bjorn Berg, University of Sao Paulo, Brazil. [Enteropneusta].
C. Burdon Jones, School of Biological Sciences, University of Townsville, Australia. [Enteropneusta].
Thomas, I. M., University of Adelaide, Australia. [Enteropneusta].
Cyprian Kulick, Institute of Paleozoology, Polish Academy of Zoology, Warsaw. [Ptrerobranchia] .
