The Collaborative International Dictionary of English v.0.48:

Cyphonautes \Cyph`o*nau"tes\ (s?f`?-n?"t?z), n. [NL., fr. Gr.
   ??? bent + ???? sailor.] (Zool.)
   The free-swimming, bivalve larva of certain Bryozoa.
   [1913 Webster]