What is "pteropoda"

Pteropoda \Pte*rop"o*da\, n. pl. [NL.] (Zo["o]l.) 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.

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.

Pteropoda ( common name pteropods, from the Greek meaning "wing-foot") are specialized free-swimming pelagic sea snails and sea slugs, marine opisthobranch gastropods. The monophyly of Pteropoda is the subject of a lengthy debate; they have even been considered as paraphyletic with respect to cephalopods. Current consensus, guided by molecular studies, leans towards interpreting the group as monophyletic.

Pteropoda encompasses the two clades Thecosomata, the sea butterflies, and Gymnosomata, the sea angels. The Thecosomata ( "case-body") have a shell, while the Gymnosomata ("naked body") do not. The two clades may or may not be sister taxa; if not, their similarity (in that they are both pelagic, small, and transparent, and both groups swim using wing-like flaps ( parapodia) which protrude from their bodies) may reflect adaptation to their particular lifestyle.