The Collaborative International Dictionary of English v.0.48:

Rotella \Ro*tel"la\, n. [NL., dim. of rota wheel; cf. LL.
   rotella a little whell.] (Zool.)
   Any one of numerous species of small, polished, brightcolored
   gastropods of the genus Rotella, native of tropical seas.
   [1913 Webster]