220 THE SPONGES OF THE WEST-CENTRAL PACIFIC 



GENUS AKA de Laubenfels 

 Aka trachys, new- 

 Text Figure No. 151 



This species is here represented by the following : 

 U.S.N. M. No. 23146, My No. M. 530, here designated as type, collected 

 September 20, 1949, by diver at the extreme south tip of Guam from the 

 Cocos Islet lagoon, sometimes called Merizo Bay. The depth was 2 

 meters, and the substrate was dead coral. 



Text Figure No. 151. Spicule (acanthoxea) 

 of Aka trachys, X 782. 



The size of the tunnels of this species are less than 1 mm in diameter, 

 and the indications are that it is not very common through the Marianas. It 

 may or may not be the only boring sponge present there. 



The color in life was yellow, and the consistency was mediocre. 



The spicules consist only of acanthostyles 4 /x by 70 p, in dimensions. 



This species is unique within the genus Aka for the extreme spininess or 

 roughness of its spicules. 



The species name selected is derived from a Greek word meaning 

 "rough." 



FAMILY PLACOSPONGIIDAE Gray 



GENUS PLACOSPONGIA Gray 



Placospongia melobesioides Gray 



Text Figure No. 152 



This species is here represented by the following: 

 U.S.N.M. No. 23040, My No. M. 419, collected July 30, 1949, by diver in 

 northwest Ponape in the lagoon near the shore. The depth was 3 meters, 

 and the substrate was dead coral. 



This is a cylindrical sponge, 2 cm in diameter and 12 cm high. 



The ectosome and endosome color in life was dark brown, and the con- 

 sistency was that of a stony hard cortex over a mediocre interior. 



The surface is relatively smooth, but covered with flat polygonal plates 

 about 12 by 20 mm in dimensions. The ramifying cracks between them are 

 about 1 mm wide, and they contain the pores and oscules. The exhalant and 

 inhalant openings cannot readily be distinguished from one another and are 

 microscopic and contractile. 



The ectosome consists of a dense, stony amalgamation of microscleres, 

 connected firmly to each other by fibrous or protoplasmic structures. The 

 endosome is microcavernous, with spicules and other structure chiefly in 

 confusion. 



