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The members of the order Conchosttaca look like miniature bivalves in general appearance. Hence, they are popularly referred to as 'clam shrimps' The conchostracans are seldom found in marine and brackish water environments. They are known to be distributed only in freShwaters.
Conchostracans are widely distributed in ephemeral water bodies. They occur in rain water puddles, rocky pools, seasonal ponds and also abundantly in fish culture ponds in South India. The clam shrimps rarely occur in bigger waterbodies and flowing water bodies with only a few exceptions like the genera Cyclestheria and Lynceus.
Some of the conchostracans are widely distributed and known to occur both in temperate and tropical regions. They are however, not known from the Antarctica region. The genera such as Leptestheria, Leptestheriella, Eocyzicus, Caenestheria, Caenestheriella, are predominantly distributed in tropical regions.
The conchostracan, Cyclestheria hislopi appear in the gut contents of camivorus fish. As such, they form food for them. At the outlets of the fish ponds, the appearance of the conchostracans in abundance may fonn a menace to the fish farmers.
There are about 200 species of conchostracans known all over the world (Belk, 1982). These species can be categorised into five families, viz., Lynceidae (Lynceus), Limnadiidae (Eulimnadia, Imnadia, Limnadia, Limnadiopsis, Limnadiopsium, and Metalimnadia). Cyclestberiidae (Cyclestheria), Leptestheriidae (Eoleptestheria, Lepteslheria, Leptestheriella, Sewellestheria) and Cyzicidae (Caenestheria, Caenestheriella, Cyzicus, Eocyzicus). Most of the species are ~escribed based on intraspecific variations. Species level taxonomy in Conhostraca is in need of clarification (Belle, 1982).
Studies from Different Environs
There are about 33 species of conchostracans known from India. These species belong to nine genera; viz. Cyclestheria (1), Lynceus ('2), Eulimnadia (5), Leptestheria (5), Leptestheriella (5), Sewellestheria (1), Caenestheria (3), Caenestheriella (5), and Eocyzicus (6). Baird (1849, 1859, 1860) recorded five species viz., Estheria polila, Caenestheriella boysi, Caenestheriella similis, Cyclestheria hislopi (from Nagpur), and Eulimnadia compressa from several places in India. Sars (1900) recorded Cyclestheria hislopi, Eulimnadia gibba, E. similis, Leptesrheriella nobilis and L. hendersoni from India. Caenestheriella indica is reported from Mandapam by Gurney (1906).
He also reported Lynceus brachyura (0. F. Muller) and Estheria davidi Simon from Indian subcontinent. In his monograph on the World Conchostraca, Daday (1913, 15, 23 &26) redescribed several species recorded from India and added two more species: Caenestheriella annandalei and Leptestheriella sarsi to the then existing list. Gurney (1930) recorded a species, Lynceus dendiculatus from South India. Bond (1934), in his detailed report on the phyllopod fauna of the Indian empire, recorded Eulimnadia margaretae, Eocygicus hutchinsoni and Eocyzicus dete"ana. Karande and Inamdar (1960) recorded Leptestheriella gigas and subsequently they (1965) reported an unidentified Eocyzicus sp. from Panchagani, Bombay. Tiwari (1959 & 66) recorded Leptestheria jaisaimerensis, Eocyzicus pellucidus, Caenestheria misrai, Caenestheriella roonwali, Leptestheria biswasi and Sewellestheria sambharensis from North India.
Nayar (1965) described M.K. Durga Prasad, DepL of Zoology, Nagatiuna University, Nagatiuna Nagar Eulimnadia ovata and Lepteslheria longispina and Nayar and Nair (1968) recorded Eulimnadia michaeli and Leptestheriella maduraensis from SOuth India. Royan and Alfred (1971) described Lynceus serratus from Madurai region. Subsequently, Royan and Sumitra (1971) reported Eocyzicus plumosus from Madurai, South India. Das and Akhtar (1971) described Eocyzicus wulari from Kashmir. Radhakrishna and Durga Prasad (1976) reported Eulimnadia gunturensis from Guntur, South India. Durga Prasad (Thesis unpubl., 1981) recorded Leptestheriella nobilis, Caenestheriella indica, and Cycleslheria hislopi from Guntur district and its environs. Recently, Battish (1981) recorded Lynceus vasishti, Leptestheria sp. indet., Eulimnadia ovata inversa. Eulimnadia sp. indeL, Caenestheriella ludhianata and Eocyzicus dhilloni from Punjab. Durga Prasad (1982) redescribed Caenestheriella indica collected from various localities in India
Curiously many Indian conchostracans described by the earlier authors are based on very stray collections. Further, some species were erected on the basis of characters which may vary with age. The species, Lynceus serrata (Royan & Alfred, 1971) is. described without consulting the descriptions of the closely allied nominal species Lynceus denticulatus (G~ey, 1930). Hence, the description of L. serrata appears to be more or less identical to denticulatus. Further, for several conchostracan species, the type material is not easily available. Similarly, the type locality is not mentioned in the descriptions of some conchostracans. These points make it difficult to .study the Indian conchostracans. Hence, a serious attention has to be paid by the future workers to these points while studying the conchostracan taxonomy.
M. K. Durga Prasad, Department of Zoology, Nagarjuna University, Nagarjuna Nagar
Barnard, K. H., 1929. Contribution to the crustacean fauna of South Africa No. 10. A revision of South African branchiopods. Ann. S. Afr. Mus. 29 : 181-272.
Bond, R. M., 1934. Report on phyllopod crustacea (Anostraca, Notostraca and Conchostraca) including a revision of the Anostraca of Indian empire. Mem. Connecticut Academy of Arts and Science, 10 : 29-62.
Daday, E. V., 1915..Monographie systematique des phyllopodes Conc.hostraces. Ann. Sci. Nat. Zool. Sere 9, 20 : 39-330.
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Royan, J. P., 1973. Conchostraca. In : A guide to the study of freshwater organisms. J. Madurai Univ. -(Suppl.) 1 : 47-70.
Sars, G. 0., 1900. On some Indian Phyllopoda. Arch. Mat. Nalurvidenskas., 22(9) : 3-30.
Tiwari, K. K., 1959~ New species of Conchostraca (Crustacea: Phyllopoda) from Rajasthan. Proc. First AliIndia Congr. Zool. t pp. 180-190.