206 



asph 



csph 



Figure 158: Ophiothrix fragilis (McBride, 1907). 



Longitudinal section of the pluteus II stage. 



adb — adoral band; alb — anterolateral band; asph — anal sphincter; csph — cardiac sphincter; 



e — esophagus; hg — hind gut; oc — oral cavity; pob — postoral band; psph — 



pyloric sphincter; s — stomach. 



appearaii' e is associated with the commencement of metamorphosis, when 

 growth of the juvenile begins, and the larva becomes heavier. 



Nervous system and sense organs : In larvae of many species of brittle 

 stars an accumulation of pigment granules is seen at the tips of the arms and 

 in the body alongside the stomach. The pigmentation may be reddish, yellow- 

 ish, or greenish. It may be suggested that the cells containing the pigment 

 granules perform the function of photoreceptors, analogous to what has been 

 described by Ryberg and Lundgren (1979) in sea urchins. 



Among the rudiments of the definitive organs in the ophiopluteus II stage, 

 we can mention the processes of the hydrocoel and the first spicules of the 

 definitive skeleton. 



METAMORPHOSIS 



In brittle stars metamorphosis occurs in free-swimming plutei. The de- 

 finitive brittle star develops on the ventral side of the larva and the fially 



