Source : Webster's Revised Unabridged Dictionary (1913)

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

Source : WordNet®

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