VII. FAUNA SYMBIOTICA INDICA. 



No. 5. — Some Sponges commonly associated with Oysters 

 AND Mussels in Madras Harbour and the Chilka Lake. 



Bv N. Annandale, D.Sc, F.A.S.B., Superintendent, 

 Indian Museum. 



(Plates X, XL) 



The sponges described in this paper all occur commonly on 

 living shells of Ostrea and Mytilus either in the harbour of Madras 

 or in lagoons of brackish water on the east coast of India. There 

 is no evidence that any one of them is invariably associated with 

 any one genus or species of mollusc, or with molluscs at all. 

 Indeed, we know that one of them [Suherites aquaedulcioris) is not 

 always associated with molluscs. But the fact that an association 

 of the kind is common, although it is not exclusive, is of con- 

 siderable interest, and, as I stated in the introduction to this series 

 of papers {Rcc. Ind. Mus. V, p. 123), I propose to deal in it with 

 associations of varying degrees of intimacy. 



From the systematic and geographical point of view th? 

 interest of the sponges lies in the fact that they are from a region 

 hitherto practically unexplored so far as the Porifera are con- 

 cerned. The multitudinous species that are found in the Gulf 

 of Manaar have been described in a series of papers by Bower- 

 bank,^ by Carter* and by Dendy '^ and the marine sponges of 

 Ceylon are now at least as well known as those of any other 

 tropical country ; but those that form a part of the much less 

 luxuriant fauna of the littoral zone north of Palk Straits have 

 hitherto almost escaped the notice of zoologists. 



The biological differences between the portions of the east 

 coast of India that lie respectivel}^ north and south of Palk Straits 

 are much greater than is perhaps as a rule realized. In the one we 

 have a sea full of coral reefs ; in the other an almost uninterrupted 

 stretch of barren sand and mud. It is only at a few places, 

 notably in the harbour of Madras, that any solid support for fixed 

 sedentar}' organisms exists, and there it is mostly artificial. 



' Pi-oc. Zool. Soc. London, 1873, p. 25. 



^ Ann. Mag. Nat. Hist. ( «; > V, p. 4^7 ; \'I, pp. t,^ and 12Q ( 1S80) and VII, 

 p. 361 (1881). 



3 Ann. Mag. Nat. Hist. (5) XX, p. 153 (1887) and 16) III, p. 73 ( 1889) ; 

 Herd man's Pearl Oyster Fisheries III, p. 57 i'lQOS). 



