THE SPONGES OF THE WEST-CENTRAL PACIFIC 239 



GENUS MYRIASTRA Sollas 

 Myriastra purpurea (Ridley) de Laubenfels 



Text Figure No. 164 



This species is here represented by the following: 

 U.S.N.M. No. 22979, My No. M. 356, collected July 5, 1949, by diver from 



the Pearl Pool in the west portion of the lagoon at Ebon Atoll. The depth 



was 3 meters, and the substrate was dead coral. 

 U.S.N.M. No. 22988, My No. M. 366, collected July 5, 1949, by diver from 



the miniature lagoon in the south portion of the lagoon at Ebon Atoll. 



The depth was 2 meters, and the substrate was dead coral. 



This species is cake-shaped or slightly lobate, about 2 mm thick and 3 to 5 

 mm in diameter. 



The exterior color in life was dull maroon to purple. This maintained 

 itself moderately well in alcohol, which became tinted with green. The interior 

 was pale yellowish drab. The consistency was between cartilaginous and 

 spongy. 



The surface is tuberculate to microhispid, slightly rough and uneven. 

 The pores are closed and must have been very small. Oscules up to 2 mm 

 in diameter can be found near the edge of the mass but in very small numbers. 



The ectosome is a dense cartilaginous cortex about 0.5 mm thick. The 

 endosome is radiate in structure and microcavernous. 



The skeleton consists first of oxeas, about 11 /x by 660 fx and second of 

 plagiotriaenes with rhabds about 10 \x by 600 jx and clads about 10 /i by 60 /x 

 to 11 ix by 70 /j,. There are also numerous anatriaenes with rhabds about 

 8 fi by 500 ix and clads about 8 \x by 26 /x. In Specimen No. M. 366, these are 

 so strongly curved that their points almost come back to touch the rhabd. The 

 protriaenes (which are probably present) were not found. The microscleres 

 are quite characteristic of the species purpurea, but they are astonishingly rare. 

 In No. M. 356, only one was discovered. This is a eutylaster, 12 jx in diameter. 

 In No. M. 366, these asters are somewhat more common but are still to be 

 described as rare. Some are as large as 12 /x, but some are as small as 3 fx in 

 total diameter. 



D 



Text Figure No. 164. Spicules of Myriastra purpurea. A: Oxea, X 182. B: Plagiotria- 

 ene, X 182. C: Cladome of anatriaene, X 182. D: Tylaster, X 782. 



