The Collaborative International Dictionary of English v.0.48:

Brittle star \Brit"tle star`\ (br[i^]t"t'l st[aum]r`), (Zool.)
   Any species of ophiuran starfishes. See Ophiuroidea.
   [1913 Webster]

WordNet (r) 3.0 (2006):

brittle star
    n 1: an animal resembling a starfish with fragile whiplike arms
         radiating from a small central disc [syn: brittle star,
         brittle-star, serpent star]