THE SPONGES OF THE WEST-CENTRAL PACIFIC 221 



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E 



4i^ 3# ° 



Text Figure No. 152. Spicules of Placospongia melobcsioidcs. A: Tylostyle, X 182. 

 B: Selenaster, X 182. C: Selenaster, X 782; only some of the rays are drawn— they 

 practically cover the surface. D: Immature selenaster, X 782. E: Siliceous spheres, 



X 782. 



The skeleton comprises megascleres which are tylostyles 10 /x by 800 tt 

 in dimensions, and exceedingly numerous microscleres which occur chiefly in 

 the ectosome. These have been called selenasters but are very much like 

 sterrasters, except that they are flattened rather than globular. These spicules 

 are about 60 /x long and wide but are only some 20 ii thick. They are densely 

 covered with spiny tubercles, almost like little stars. The shape is not evenly 

 rounded, but there is at one point an indentation or hilum, so that the shape 

 is rather like that of a bean. 



The immature selenasters are essentially spirasters. Many descriptions of 

 species of Placospongia list spirasters as part of the spiculation, but it may be 

 that the microscleres thus designated were merely juvenile selenasters. 



The species melobesioides has as one distinctive trait, the occurrence of 

 microscopic siliceous spheres. These may represent the centrums of spher- 

 asters from which all the spines or rays are missing. In the specimens from 

 Ponape, these microscleres are only 2 /x in diameter. 



This species was first described by Gray, 1867, page 127, from the East 

 Indian region. Schmidt, 1870, page 72, extended its known range to Florida, 

 and de Laubenfels, 1936, page 154, confirmed this. Thiele found it in 1898 in 

 Celebes of the East Indies. It may be circumequatorial. 



ORDER EPIPOLASIDA Sollas 



FAMILY JASPIDAE de Laubenfels 



GENUS STELLETTINOPSIS Carter 



Stellettinopsis isis, new 



Text Figure No. 153 

 Plate X, Figure a 



This species is here represented by the following : 

 U.S.N.M. No. 23137, My No. M. 520, here designated as type, collected 

 September 9, 1949, by divers near Malakal Islet in the Palaus. The depth 

 was 3 meters, and the substrate was fragments of dead coral. 



