CLADOCERANS ( CRUSTACEA : BRANCHIOPODA : CLADOCERA ) FROM ASSAM ( N . E . INDIA )

Taxonomic studies on the Indian Freshwater Cladocera began nearly one and a half century ago and since then these entomostraceous crustaceans have been documented from scattered localities from distant parts of this country (Sharma and Michael, 1987; Michael and Sharma, 1988; Sharma, 1991). The faunal investigations on cladocerans from different states of Northeastern India in general and that of Assam, in particular, are relatively fewer save for the studies by Patil (1976), Biswas (1980), Sharma and Sharma (1999, 2008) and Sharma (2008) while Michael and Sharma, 1988 referred to limited collections from N.E. region.


INTRODUCTION
Taxonomic studies on the Indian Freshwater Cladocera began nearly one and a half century ago and since then these entomostraceous crustaceans have been documented from scattered localities from distant parts of this country (Sharma and Michael, 1987;Michael and Sharma, 1988;Sharma, 1991).The faunal investigations on cladocerans from different states of Northeastern India in general and that of Assam, in particular, are relatively fewer save for the studies by Patil (1976), Biswas (1980), Sharma andSharma (1999, 2008) and Sharma (2008) while Michael and Sharma, 1988 referred to limited collections from N.E.region.
While working on zooplankton samples collected from the floodplain lakes (beels) of Assam, the authors came across nine interesting species of Cladocera, including four new records from North-Eastern India and five new records from Assam.All the recorded taxa are briefly diagnosed and illustrated, and remarks are made on their distribution.

MATERIALS AND METHODS
The present observations are based on plankton samples collected, during July, 2007-August, 2008, from floodplain lakes of Assam.All the samples were collected with nylobolt plankton net (No. 25) and preserved in 5% formalin.Individual collections were screened with a Wild-stereoscope binocular microscope.
Various cladocerans and their disarticulated appendages were mounted in Polyvinyl alcohollectophenol mixture.The details of head pores and their arrangements in the Chydorids were studied following Megard (1965).
Remarks : Represents a new record from Assam.Distribution: India: Rajasthan, Kerala, Tamil Nadu, Maharashtra, Gujarat.Elsewhere: Sri Lanka, China, Java, East Africa and South America.str.by rounded pits or tubercles on its head shield and valves.
Remarks : Represents a new record from Assam.
tropicum can be diagnosed correctly from D. modigliani by its characteristic features, geographical distribution and preference for different aquatic environs.In addition, this species is confused (Korovchinsky, 2000) with D. dubium Manuilova (= D. dubia, name amended by Korovchinsky and Mirabdullaev, 1994).Further, D.
tropicum is a relatively large bodied species of the genus Diaphanosoma; its large size may negatively affect distribution of such taxa in tropical waters, with high predation pressure (Kerfoot and Lynch, 1987;Gliwicz, 1994).Nevertheless, its long swimming antenna and massive muscles testify to good swimming ability, which perhaps helps it to co-exist with predators (Korovchinsky 2000).Interestingly, D. tropicum is so far known to occur in India only from Tamil Nadu.The present study, the second confirmed report of this interesting species from India, considerably extends its distributional range to N.E.region and, hence, reflects presence of distant disjunct populations of the species in this country.
The sole earlier report of this genus from Asia refers to Latonopsis fernandoi-a new species described by Rane (1983) from Madhya Pradesh which was, in turn, treated as a synonym of Sarsilatona serricauda (Sars) by Sharma and Sharma (1990).The specimens of S.
Alona verrucosa are new records from Northeastern India while Streblocerus serricaudatus, Alonella clathratula, Alona guttata tuberculata, A. monacantha tridentata and A. pulchella are new records from Assam.