THE SPONGES OF THE WEST-CENTRAL PACIFIC 53 



The skeleton consists of fibers usually about 20 p in diameter but oc- 

 casionally thicker, up to perhaps 40 p. These are of clear spongin resembling 

 that of the commercial sponges. Here and there in these fibers, but quite 

 rare, there are isolated spicules which are thin oxeas, measuring 1 p by 88 p. 



The genus Acervochalina is set off from the genus Haliclona by its 

 copious slime production. The type Spongia limbata is British and is 

 dull colored. Another species, originally described as Chalina finitima by 

 O. Schmidt, is West Indian and also is dull colored. Ridley has recorded 

 the latter from the Indian Ocean and the Australian region. A possibility 

 exists that those thus recorded really belong to the present species and not at 

 all to finitima. The present species is set apart from others in the genus by 

 the blue color and almost complete lack of proper spicules. 



GENUS HALICLONA Grant 



This genus is one of the most important in the phylum Porifera, and is 

 also one which is in considerable systematic confusion. It was established by 

 Grant, 1841, page 5, for the species ocidata. This is a well-known sponge, 

 first described as Spongia oculata by Linne, 1759, page 1348. The genus, 

 well characterized by its type, is abundantly represented throughout the 

 tropical oceans, including the territory studied in the present report. These 

 are sponges whose megascleres are only oxeas, which never have any micros- 

 cleres, and whose surface is peculiarly devoid of any specialization. There 

 are no subdermal canals parallel to the surface, no dermal skeleton ; the endo- 

 some simply stops and that is the surface. The spicules are always more or 

 less isodictyal in arrangement — connected to one another at their tips by 

 more or less spongin, forming triangular or polygonal meshes on each side 

 of which is a single spicule. There are usually also present fascicular 

 strands of spicules which are more or less encased in cylindrical fibers of 

 spongin. The genotype is -a much-branched ramose sponge. Many others 

 are of this type, but about as many sponges which may or may not be con- 

 generic are incrusting. 



Are two or more genera involved ? Many authors have used a separate 

 name (Reniera) for the incrusting forms. As against this, there are species 

 such as viridis which is occasionally incrusting although typically ramose. 

 With this species, the difference is certainly ecological. Is it thus for the 

 others? It seems likely (but far from certain) that many species are ge- 

 netically incrusting. I believe that at least subgeneric status should be main- 

 tained for the usually ramose, more fibrous species in contrast to the always 

 (or usually) incrusting, less fibrous species. The fact that some tend toward a 

 middle ground does not constitute refutation, because we have reason to 

 believe that in the geologic past (it not today) intermediates existed between 

 each animal in the world and every other one ; this is the premise of evolution. 



