The Collaborative International Dictionary of English v.0.48:

Asiphonea \As`i*pho"ne*a\, Asiphonata \A*si`pho*na"ta\,
Asiphonida \As`i*phon"i*da\, n. pl. [NL., fr. Gr. 'a priv. + ? a
   tube.] (Zool.)
   A group of bivalve mollusks destitute of siphons, as the
   oyster; the asiphonate mollusks.
   [1913 Webster]