The Collaborative International Dictionary of English v.0.48:

Pteropoda \Pte*rop"o*da\, n. pl. [NL.] (Zool.)
   A class of Mollusca in which the anterior lobes of the foot
   are developed in the form of broad, thin, winglike organs,
   with which they swim at near the surface of the sea.
   [1913 Webster]

   Note: The Pteropoda are divided into two orders:
         Cymnosomata, which have the body entirely naked and
         the head distinct from the wings; and Thecosomata,
         which have a delicate transparent shell of various
         forms, and the head not distinct from the wings.
         [1913 Webster]