258 



THE SPONGES OF THE WEST-CENTRAL PACIFIC 



Text Figure No. 181. Spicules of Leuconia tropica, X 90, after Tanita. A: Oxea. 

 B: Ectosomal triact. C : Tubar triact. D: Tetract, in this case from the wall of one of 



the larger exhalant canals. 



The shape is subspherical, with a large central cloaca, and the size is 

 about 2 cm in diameter. 



The color in preservation is yellowish white, and the consistency brittle 

 and rigid. 



The surface is hispid, and the size of pores is not given ; but the oscules 

 (or at least the upper opening of the cloaca) may be as much as 12 mm in 

 diameter. 



The dermal structures are very thin, and the endosome exhibits a 

 typical rhagon architecture, with flagellate chambers as much as 100 ft to 

 145 (i in diameter. The skeleton comprises dermal triacts tangentally placed, 

 and tetracts with three rays tangental and the fourth piercing down into the 

 chamber layer. The rays are about 16 /x by 300 p.. In the chamber layer there 

 are large triaxons with rays about 50 fi by 300 /x in dimensions. Lining the 

 cloaca, there are small tangentally placed triaxons and also tetraxons — some 

 of which have a small ray penetrating into the cavity, others of which have a 

 longer ray penetrating back into the chamber layer. Many of the rays are 

 about 12 ti by 400 ft. 



This species was described by Senji Tanita, 1943, page 434. He states 

 "the main characteristic of this species is the presence of dermal quadri- 

 radiates with apical rays protruding not very deeply into the chamber layer. 

 In this point the present species bears a close resemblance to Leucandra 

 thulakomorpha Row and Hozawa, 1931, page 791 ; but it differs from the 

 latter in the presence of subgastral radiates, and the larger size of tubae 



