O'PHIUROI'DEA (Neo-Lat. nom. pl., from Ok. four, ()phis. serpent
apd, our," thin. 'rhe class of brittle stars. or sand stars, of
which Ophiura is the typical genus. Ophiuroids (or ophiurans I
are star-shaped, freely moving echino Berms (q.v.), with a flat,
roundish or polygonal disk, from which suddenly arise live arms,
which are slender, cylindrical, and contain no spacious
continuation of the etelomie cavity of the disk, or hepatic
ewea, while there is no vent. '11w re are no ambulacral grooN es
in the arms, and the suckers are but little used in locomotion,
whicl is mainly effected by the arms themselves, the 'feet,' or
ambulacra, being thrust out laterally and acting as tactile
organs. The mouth and also the madreporite are on the under side
of the disk. On the ventral surface, also, are five slits which
connect with a corresponding number of respiratory saes (bursa.)
into which the ovaries or spermaries open. The eggs passing out
through these slits are fertilized in the water, the sexes being
distinct.