The Collaborative International Dictionary of English v.0.48:

Argonauta \Ar`go*nau"ta\, n. (Zool.)
   A genus of Cephalopoda. The shell is called paper nautilus
   or paper sailor.
   [1913 Webster]

   Note: The animal has much resemblance to an Octopus. It has
         eight arms, two of which are expanded at the end and
         clasp the shell, but are never elevated in the air for
         sails as was formerly supposed. The creature swims
         beneath the surface by means of a jet of water, like
         other cephalopods. The male has no shell, and is much
         smaller than the female. See Hectocotylus.
         [1913 Webster]

WordNet (r) 3.0 (2006):

Argonauta
    n 1: type genus of the family Argonautidae: paper nautilus [syn:
         Argonauta, genus Argonauta]