The Collaborative International Dictionary of English v.0.48:

Holothurian \Hol`o*thu"ri*an\, a. (Zool.)
   Belonging to the Holothurioidea. -- n. One of the
   Holothurioidea.
   [1913 Webster]

   Note: Some of the species of Holothurians are called sea
         cucumbers, sea slugs, trepang, and b[^e]che de
         m[`e]r. Many are used as food, esp. by the Chinese.
         See Trepang.
         [1913 Webster]

WordNet (r) 3.0 (2006):

holothurian
    n 1: echinoderm having a flexible sausage-shaped body, tentacles
         surrounding the mouth and tube feet; free-living mud
         feeders [syn: sea cucumber, holothurian]