pteropoda

from The Century Dictionary.

• A division of Mollusca, having the mesopodium or middle part of the podium or foot expanded into a pair of large alate lobes like wings or flippers, and used as such to swim with; the pteropods.
• In De Blainville's classification (1825), one of two families of his fifth order, Nucleobranchiata (the other being Nectopoda), composed of the genera Atlanta, Spiratella, and Argonauta. It is thus a highly artificial group, comprising a part of the heteropods together with some cephalopods, etc.

from the GNU version of the Collaborative International Dictionary of English.

• noun plural (Zoöl.) 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.