THE SPONGES OF THE WEST-CENTRAL PACIFIC 297 



the Australian-East Indian region is a somewhat predominately related area. 

 If the shallow water sponges of the Philippines were better known, much 

 relationship might be found with them. 



Yet the East Indian region is so slightly predominant as to attract at- 

 tention. Out of 77 species known to occur outside the area studied, 24 or 

 nearly a third occur in the West Indies. The more sponges are studied, the 

 more we find new species which occur in only one small locality. On the other 

 hand, species which were previously known to be fairly widespread are more 

 and more discovered to be actually circumequatorial. Apparently most sponge 

 species have either extremely narrow distribution, or else are practically 

 cosmopolitan. 



The somewhat predominant East Indian influence upon the fauna of the 

 West Central Pacific may well be influenced by the counter-equatorial cur- 

 rent which flows eastward toward this region from the Philippines (see 

 de Laubenfels, 1950, page 256, and following). On each side of it, the north 

 and south equatorial currents flow toward the west. I had hoped to find more 

 conspicuous distributional patterns of sponge species and, therefore, investi- 

 gated currents carefully, but the evidence points to very thorough dispersal. 

 This dispersal may be so uncertain that it happens only at geologically rare 

 intervals and requires phenomenally favorable conditions. Thus, in the long 

 intervals of nondispersal, mutations may yield species which have only local 

 distribution. Probably local extinctions are also common, as a result of storms 

 or topographical changes. It may be that each species, other than those gene- 

 rated by recent mutations, has at one time or another inhabited each and 

 every part of the whole area, but that some species have perished in one place 

 whereas other species have perished in another place. 



Ecologically, it is interesting to note how often (wherever one is in the 

 world) a certain environmental niche has its sponge of a certain appearance, 

 provided only that the ecology be the same. 



I have made extensive studies in the West Indies. There, in a certain 

 sort of setting, one finds species of Spongia. So one often does in Micronesia. 

 The same is true for Haliclonas and Callyspongias, although the species are 

 different. 



In exposed shallow water of the West Indies, one commonly finds a 

 fleshy, ramose yellow sponge. One does likewise in the Western Tropical 

 Pacific, and the sponge looks in life exactly like the matching West Indies 

 sponge. It has the same color, the same texture to the fingers, and an indis- 

 tinguishable consistency. The flesh appears to be identical. Upon dying, each 

 has the same striking tendency to turn green, then purple, then black. Yet, 

 under microscope, the fibers of the West Indian one prove to be the pith- 

 filled ones typical of Verongia, while those of the Pacific one are the debris- 

 filled fibers of Thorectopsamma. How closely are these two sponges (now put 

 in two genera) really related? 



