OPHIUROIDEA. 261 



upper and lower marginals, with skin-gills not restricted to the 

 dorsal (abactinal) surface, with narrow ambulacral plates, with 

 ambulacrals or adambulacrals prominent in the peristome, with 

 pedicellarise sessile or stalked (if present), often with apparently 

 four rows of tube-feet. 



e.g. Astt'rias, Solaster^ Henricia, Brisinga. 



Class OPHIUROIDEA. Brittle-stars, e.g. Ophiopholis 

 aculeata 



Echinoderms with a stellate flattened body, nearly related 

 to starfishes, but usually differing from them in having the 

 arms (sometimes branched) sharply marked off from the 



FIG. 135. Ventral surface of disc of an Ophiuroid 

 ( Ophiothrix fragili s). After Gegenbaur. 



-., Openings of genital pockets or bursae ; m., mouth; v., ventral 

 plates of arms ; sp., spines of arms ; tf., tube-feet at the right side 

 these are represented as retracted ; o., the openings through which 

 they are protruded ; /., plates around mouth bearing the so-called 

 teeth ; one of these plates is perforated, and functions as the 

 madreporite 



central disc, no ambulacral groove on the ventral surface of 

 the arms, the digestive organs and gonads restricted to the 

 disc, and the madreporite ventral. There is no anus. There 

 are deep respiratory clefts on the disc at the insertion of the 



