Wordnet 3.0
NOUN (1)
1.
minute sedentary marine invertebrate having a saclike body with siphons through which water enters and leaves;
The Collaborative International Dictionary of English v.0.48:
Ascidian \As*cid"i*an\, n. [Gr. ? bladder, pouch.] (Zool.)
One of the Ascidioidea, or in a more general sense, one of
the Tunicata. Also as an adj.
[1913 Webster]
WordNet (r) 3.0 (2006):
ascidian
n 1: minute sedentary marine invertebrate having a saclike body
with siphons through which water enters and leaves