92 THE SPONGES OF THE WEST-CENTRAL PACIFIC 



Text Figure No. 55. Spicules of Iotrochota pella, X 781. A: Strongyles. B: Amphidiscs. 



This species was abundant at Majuro Atoll, especially toward the eastern 

 portion of the lagoon. 



This species is incrusting, but it is very difficult to give its measurement. 

 The thickness is complicated by the fact that it is usually on ramose coral, 

 whose surface is both deeply eroded and in other places strongly protruding. 

 Certainly bits as thick as 6 cm can be found in a few places. The lateral 

 growth is indefinite, limited only by the size of the dead coral on which it is 

 placed. Many specimens often amount to as much as 40 square cm. 



In life, the color of the exterior was intense glistening black. The in- 

 terior was very dark dull green, but the green color may have been due to 

 symbionts rather than to the sponge itself. The consistency was spongy. 



The surface is conulose, but the conules vary greatly in size ; an average 

 measurement may be stated as 1 mm high and 2 mm apart. The pores are 

 about 35 n to 50 /x in diameter and about 100 [x apart, center to center. The 

 oscules could not be distinguished from the inhalant apertures. 



The ectosome consists of a thin fleshy dermis, and the endosome is also 

 very fleshy. It contains an irregular fibro-reticulation, but this is far from 

 conspicuous. 



The skeleton consists of roughened irregular fibers, about 15 [x to 60 /x 

 in diameter. Most of their extreme irregularity arises from the fact that 

 they are full of foreign debris. Some of the ascending fibers may even be 

 fascicular in nature. These fibers also contain proper megascleres, about 10 

 per cross section. These spicules are strongyles, often extremely straight, 

 but in other cases, definitely curved; some are 4 fx by 140 /x, others 3 fx by 

 180 jx, some 2 [x by 200 jx, and others measure within these ranges. The 

 microscleres are very rare, but are very symmetrical amphidiscs, or birotu- 

 lates, 17 fx long, with the discs 4 /x in diameter. The number of teeth is dif- 

 ficult to make out because of refraction patterns, but there appear to be 

 about 6 at each end. 



This species is distinctive for the extreme thinness of its spicules and 

 the abundance of foreign material, together with the resulting extreme ir- 

 regularity of the fibers. The color is probably also distinctive. Many speci- 

 mens of Iotrochota are mentioned in the literature as being black, but these 



