Studies of planktonic Ostracoda collected from Arabian Sea and Bay of Bengal

General distribution and numerical abundance of planktonic ostracods, as a whole, in the Exclusive Economic Zone of India and nearby seas based on 1086 collections (1985-'88) are discussed. The average density of ostracods in the area investigated was estimated to be 17395/1000 m . The ostracods occurred far more abundantly in the shelf waters than in the oceanic areas. Samples collected indicated that 95% of the ostracod population occurred off the west coast of India round the year. They were found remarkably high (61168/1000 m\ 63.3%) between 10°N and 15°N off the west coast, while their abundance between 10°N and 15°N off the east coast of India was the lowest (624/1000 m , 0.65%). The abundance of ostracods was always associated with monsoon when the maximum of 31920/1000 m was obtained and this was mainly due to the swarming nature of these organisms. The minimum was observed during the premonsoon period when an average of 1508/1000 m ostracods occurred. Comparison of ostracod distribution in the EEZ of India between day and night yielded values of 30.95 and 69.05% respectively, which showed that they are more abundant during night, thereby illustrating pronounced diurnal vertical migration.