166 THE SPONGES OF THE WEST-CENTRAL PACIFIC 



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Text Figure No. 108. Spicule (tylostyle) of Stylotrichophora rubra, X 782. 



lagoon. The depth was 5 meters, and the substrate was dead coral. 

 This is one of the species which occur usually on the underside of the 

 coral. It was abundant in Ebon Atoll. 



This is an incrusting sponge, usually only about 300 p thick, spreading 

 laterally indefinitely, though most of its incrustations were less than 3 cm 

 across. 



The color in life was brilliant red, and the consistency a colloidal sol. 

 It is remarkable to note, however, that upon placing the specimen in alcohol, 

 this consistency changed to become quite tough — an alteration which is not 

 to be expected. 



The surface is shiny smooth and lipostomous. 



The ectosome comprises a very definite dermis, 10 p to 40 p thick, 

 containing foreign material, particularly bits of dead Bryozoa. The endo- 

 some is well provided with flagellate chambers, 50 ju to 60 jn in diameter, 

 and also contains spicular tracts. 



The skeleton includes spongin uniting spicules into tracts which are not 

 at all echinated but which contain some spicules and even more foreign 

 material, such as small bits of sand. These fibers or tracts are about 25 p 

 in diameter. The spicules consist of smooth straight tylostyles with heads 

 only slightly greater in diameter than the shaft but quite long in the direction 

 of the long axis of the shaft. It appears as though this enlargement was 

 brought about almost entirely by an enlargement of the axial canal of the 

 spicule, as a result of which, from whatever angle the spicule is viewed, there 

 is a strong resemblance to a needle with an eye in the regular place. These 

 spicules vary from 3 ju, by 220 p to 4 p by 230 ju, in dimensions. Numerous 

 raphides, 0.2 p. by 40 p., also are present. 



This species was first described as Stylotrichophora rubra by Dendy, 

 1895, page 259, from Australia. Dendy did not comment on any resemblance 

 of the spicules to needles, but his description in every other respect agrees 

 remarkably closely. 



GENUS BIEMNA Gray 

 Biemna fortis (Topsent) Burton 



Text Figure No. 109 

 Plate VI, Figure b 



This species is here represented by the following: 

 U.S.N.M. No. 23034, My No. M. 413, collected July 30, 1949, by diver in 

 northwest Ponape from the lagoon near the shore. The depth was 3 

 meters, and the substrate was dead coral. 



