igi5.] Fauna of the Chilka Lake : Coelenterates. 73 



Their body-wall is thin and not particularly muscular ; they have twelve complete 

 mesenteries, an ample oral disk and a large number of slender tentacles arranged in 

 several or many cycles. For the two new genera I propose the names Pelocoetes and 

 Phytocoetes. The former, as its name indicates, is a dweller in mud, while the latter 

 lives, free or lightly attached, among weeds, in sponges or in holes in logs of wood. 

 The generic peculiarities of Pelocoetes are so marked that at first sight it might be 

 placed in a different family from Metridium. It is a typical burro wer with an elongated 

 vermiform body, and a muscular though by no means thick body-wall. Its oral 

 disk is highly specialized, the arrangement of its tentacles peculiar. Phytocoetes has 

 an elongated, but not a vermiform column. Its oral disk remains normal, but the 

 number of its tentacles, which exhibit no marked peculiarity in arrangement, is 

 somewhat reduced. In both genera little practical use is made of the aboral disk, 

 but it has not entirely disappeared and is to some extent functional. In both 

 genera, notwithstanding this fact, the lower extremity of the column bears, both 

 functionally and structurally, a remarkable resemblance to the physa of such types 

 as Edwardsia and Cerianthus that totally lack an aboral disk. 



If this were all that could be said about the three genera it would appear that 

 they were very distinct, and that Pelocoetes and Phytocoetes differed considerably, one 

 from another and both from Metridium. But an examination of the anatomy and 

 even of the external characters reveals very striking resemblances, and, although there 

 would be no difficulty in distributing a set of living anemones into their respective 

 genera, there is often a very real difficulty in sorting out specimens preserved in 

 alcohol. The colouration of the known species is identical or almost so ; all have 

 the same translucent watery appearance, the same absence of intrinsic pigment ; l 

 the arrangement of the mesenteries is the same, except that the cycles of incomplete 

 septa differ in number, while the musculature of the body- wall is very similar ; the 

 structure of the gonads, of the muscle-banners and of the individual tentacles appears 

 to be practically identical. 



The fact that these three genera live together in circumstances very unfavour- 

 able to their group as a whole (viz. in estuaries, creeks, pools and lakes in which the 

 water is much fresher than normal sea-water and subject, moreover, to great and 

 even sudden changes in salinity ; in which the bottom is composed of soft mud ; in 

 which rocks covered at all seasons and even stiff water-weeds are practically absent) 

 must not be forgotten in considering their relationships. 



Metridium schillerianum , the species originally described from the Gangetic 

 delta, maintains itself by clinging tightly to floating logs, which are by no means 

 common in the Gangetic delta, and to posts fixed on the edge of canals and creeks. 

 It is a normal member of its genus, which is probably cosmopolitan in distribution 

 and essentially marine. Of the three genera, Metridium is certainly the most primi- 

 tive and, indeed, may be the ancestral form of the other two, both of which are 



1 The colouration of all these brackish-water species appears to be due to the presence of Zoo- 

 chlorellae and of a minute purple alga in the endoderm. 



