COELENTERATES. 



By N. AnnandaIvE. 



As will be seen from the list on p. 69, we obtained specimens of sixteen species 

 of coelenterates in the Chilka Lake, viz. six Actinozoa, one Scyphomedusa and nine 

 Hydrozoa. Five of the Actinozoa are Actiniaria and one an Alcyon arian ; the 

 Scyphomedusa belongs to the order Rhizostomata ; one of the Hydrozoa is a Narco- 

 medusa and one a Siphon ophoran, while the remainder are true hydroids or hydro- 

 medusae, including four Calyptoblastea and three. Gymnoblastea. Of the Calypto- 

 blastea it is possible that a hydroid and a medusa actually represent the different 

 generations of a single true species. 



Of the Alcyonarian (a species of Virgularia probably not yet named) I propose 

 to say no more at present than that it also occurs in the Gangetic estuaries. Our 

 specimens are in the hands of a specialist, who will doubtless describe them in due 

 course. 



The Actiniaria are perhaps the most interesting group represented, for not only 

 do they include species of the primitive genera Edwardsia and Halianthus, neither of 

 which appears to have been found hitherto in the Indian Ocean, but they also 

 include two species of Metridiine Sargatiidae that are here described as the types of 

 new genera. These genera are apparently specialized for different phases of life in 

 conditions such as occur in the Chilka Lake and in the Gangetic delta. Notwith- 

 standing their high degree of apparent secondary specialization, it is possible that 

 the type-species of one of them is in reality no more than a permanent post-larval form 

 of Metridium schillerianum, long known from the estuarine tracts of the Ganges. 

 All the species of Actiniaria found in the Chilka Lake occur in its main area, in 

 which it is evident that they are permanent residents. Most of them, if not all, 

 are, however, to some extent affected by the seasonal irruption of fresh water and 

 probably only a few individuals of each survive annually to perpetuate their kind. 



The only Scyphomedusa we obtained is also a permanent inhabitant of the main 

 area of the lake, in which we have evidence that it breeds regularly, though it 

 occurs also in the Bay of Bengal. A fortunate accident made it possible to study 

 the direct effect of fresh water on the general physiology and the structure of this 

 species, not only in the Chilka Lake but more particularly in the Knnur backwater 

 near Madras. 



The Coelenterata of the lake fall into three classes biologically : (1) casual visitors 

 from the sea; (2) periodic immigrants from the Bay of Bengal; and (3) permanent 

 inhabitants of brackish water or of water subject to great changes in salinity. The 

 first group consists of a few surface or midwater forms of which individuals are 



