| Pteropoda Temporal range:
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|---|---|
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| A sea angel of the species Clione limacina | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Gastropoda |
| Clade: | Euopisthobranchia |
| Order: | Pteropoda Cuvier (1804) |
Pteropoda (common name pteropods, from the Greek meaning "wing-foot") are specialized free-swimming pelagic sea snails and sea slugs, marine opisthobranch gastropods. Most live in the top 10 m of the ocean and are less than 1 cm long. The monophyly of Pteropoda is the subject of a lengthy debate; they have even been considered as paraphyletic with respect to cephalopods.[1] Current consensus, guided by molecular studies, leans towards interpreting the group as monophyletic.[2]
Pteropoda encompasses the two clades Thecosomata, the sea butterflies, and Gymnosomata, the sea angels. The Thecosomata (lit. "case-body"[3]) 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 convergent adaptation to their particular lifestyle.
- ^ Wägele, Heike; Klussmann-Kolb, Annette; Verbeek, Eva; Schrödl, Michael (2013). "Flashback and foreshadowing – a review of the taxon Opisthobranchia". Organisms Diversity & Evolution. 14: 133–149. doi:10.1007/s13127-013-0151-5.
- ^ Klussmann-Kolb, A.; Dinapoli, A. (2006). "Systematic position of the pelagic Thecosomata and Gymnosomata within Opisthobranchia (Mollusca, Gastropoda) - revival of the Pteropoda". Journal of Zoological Systematics and Evolutionary Research. 44 (2): 118. doi:10.1111/j.1439-0469.2006.00351.x.
- ^ "theco-". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)