THE SPONGES OF THE WEST-CENTRAL PACIFIC 



145 



The species plinthina is unique within the genus Microciona for its 

 raphides. 



The name selected is derived from the Greek word for "brick." 



Microciona micronesia, new 



Text Figure No. 93 



This species is here represented by the following : 

 U.S.N.M. No. 22833, My No. M. Ill, here designated as type, collected 

 June 28, 1949, by diver at Majuro Atoll near the east end of the lagoon 

 in the vicinity of the islet called Rita or Jarej. The depth was 4 meters, 

 and the substrate was dead coral. 



This species is a thin crust, about 1 mm thick, spreading laterally at 

 least 4 cm. 



The exterior and interior color in life was medium red, and the con- 

 sistency was mediocre. 



The surface is smooth and lipostomous, characteristic of very thin in- 

 crusting sponges. 



The ectosome and endosome are not sharply marked off from each other, 

 as usual in sponges as thin as this, but the surface does show a number of 

 spicules with points outward. 



The skeleton of this species consists of large tylostyles, 9 [x by 200 /x, 

 the heads of which are only slightly enlarged but are rendered quite lumpy 

 by blunt spines. There are also smooth tylostyles, 3.5 fi by 200 /*, and com- 

 pletely acanthose echinating styles, 5 ju, by 70 /*. The microscleres include 

 abundant typical palmate isochelas, 14 /x to 16 p. long, and a few enormous 



Text Figure No. 93. Spicules o£ Microciona micronesia, X 782. A : Basal portion of one 



of the longer styles. B: Basal portion of one of the tylostyles. C: Echinating acantho- 



styles. D: Toxas. E: Two palmate isochelas, one in side view, one front view. 



