The Collaborative International Dictionary of English v.0.48:

Spirula \Spir"u*la\, n. [NL., dim. of L. spira a coil.] (Zool.)
   A genus of cephalopods having a multilocular, internal,
   siphunculated shell in the form of a flat spiral, the coils
   of which are not in contact.
   [1913 Webster]

WordNet (r) 3.0 (2006):

spirula
    n 1: a small tropical cephalopod of the genus Spirula having
         prominent eyes and short arms and a many-chambered shell
         coiled in a flat spiral [syn: spirula, Spirula peronii]