1) Tunicate 2) Urochord 3) Urochordate 
Doliolum is a genus of tunicates, the members of which move via jet propulsion. A detailed description can be found at {cite doi|10.1007/s002270050294}. The World Register of Marine Species lists the following species: ...
• (n.) A genus of freeswimming oceanic tunicates, allied to Salpa, and having alternate generations.
Do·li'o·lum noun [ Latin doliolum a small cask.] (Zoology) A genus of freeswimming oceanic tunicates, allied to Salpa , and having alternate generations. 
[n] - free-swimming oceanic tunicate with a barrel-shaped transparent body
noun free-swimming oceanic tunicate with a barrel-shaped transparent body