| dc.description.abstract | Euthecosomata (holoplanktonic opisthobranch molluscs) sorted out from the collections of the International Indian Ocean Expedition are now being studied and the present communication is a first report based on an examination of material from 395 stations Species were identified with the help of Tesch's studies (1946, 48) on the Dana Collections Limacina helicina (Phipps) is newly recorded from the Indian Ocean Including it, twenty-five species of euthecosomes are known to occur in this Ocean This paper reports on twenty species, their distribution and numerical abundance over the Indian Ocean and compares present results with earlier records of the group in the Indian Ocean The occurrence of a greater number of species as well as of larger numbers of individuals of particular species, is noted from the following areas: the sea east of Somalia, the Mozambique channel, the equatorial belt of the Indian Ocean, specified areas of the Arabian sea and Bay of Bengal The most noteworthy of these areas is to the east of Somalia from where consistently high numbers of individuals were obtained for a good many species This area is well-known for the upwelling of nutrient rich water during the south-west monsoon period and for its high biological productivity A comparison of different months of the year with respect to the numerical abundance of three species of Limacina, indicated that all three species were at maximum abundance during August, which is the peak period of the south-west monsoon Some species, e.g., Styliola subula, Cuvierina columnella, Cavolinia globulosa and C inflexa, that are common in the equatorial belt and in Somali waters, are rare in the Bay of Bengal and the Arabian Sea, but the reasons for this are yet to be unravelled | |
