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 
pedicellariz sessile or stalked (if present), often with apparently 
four rows of tube-feet. 
e.g. Asterias, 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 
Fic. 135.—Ventral surface of disc of an Ophiuroid 
(Ophiothrex fragilis).—After Gegenbaur. 
&, Openings.of genital pockets or burse; 7., mouth; v., ventral 
plates of arms; s/., spines of arms ; ¢/, tube-feet—at the right side 
these are represented as retracted; 0., 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 dise at the insertion of the 
