THE SPONGES OF THE WEST-CENTRAL PACIFIC 



121 



The skeleton consists almost exclusively of spicules and colloidal ma- 

 terial. The commonest megascleres are acanthoxeas ranging from 5 fx by 

 300 fx to 9 ,u, by 620 fx in dimensions. The spines are exceedingly abundant 

 and very minute, and in the smaller spicules the spines are confined to the 

 small region near the ends of the spicule. The second type of megasclere is 

 a smooth strongyle 8 /x by 400 fx to 13 fx by 710 /a in dimensions. These are 

 not particularly localized but do seem to be a little more predominant in the 

 ectosome than in the endosome. The microscleres are tylotes with very con- 

 spicuous, relatively large spherical heads. They range in size from 1 ju, by 

 60 jx to 2 fx by 140 fx in dimensions of the shafts. The heads in either case 

 are at least 1 fx greater in diameter than the shaft. 



This species is sharply set off from the only other one in the genus 

 Myrmekioderma by possession of these distinctive microscleres. The species 

 name tylota is derived from their presence. 



Myrmekioderma granidata (Esper) Ehlers 



Text Figure No. 75 



This species is here represented by the following : 

 U.S.N.M. No. 23073, My No. M. 453, collected August 10, 1949, by diver 

 in Truk lagoon near Moen Island. The depth was 4 meters, and the 

 substrate was dead coral. 



The shape is massive and the size much larger than any of those of the 

 preceding species, but only the one specimen was found in the Truk lagoon. 



D 



Text Figure No. 75. Spicules of Myrmekioderma granulata. A: Acanthoxea of the 

 abundant type, X 182. B: Less common type of oxea, X 182. C: One end of a spicule 

 such as A, but X 781. D: One end of a spicule such as B, but X 781. E: Raphides, 



X 781. 



