Doliolum

from WordNet (r) 3.0 (2006)

doliolum
    n 1: free-swimming oceanic tunicate with a barrel-shaped
         transparent body

from The Collaborative International Dictionary of English v.0.48

Doliolum \Do*li"o*lum\, n. [L. doliolum a small cask.] (Zool.)
   A genus of freeswimming oceanic tunicates, allied to {Salpa},
   and having alternate generations.
   [1913 Webster]