pteropod

Etymology

From Ancient Greek πτερόν (pterón, “wing, feather”) + ποδός (podós), genitive singular of πούς (poús, “foot, leg”). Equivalent to ptero- + -pod.

noun

1. Any of free-swimming pelagic sea snails and sea slugs, of the suborder Thecosomata, that have winglike lobes on the feet; a sea butterfly.
   Pteropods, also known as sea butterflies, are marine gastropods adapted to pelagic life.[…]When pteropods constitute a high percentage of the ooze the deposit is called pteropod ooze. 1998, Yvonne Herman, “5: Pteropods”, in B.U. Haq, A. Boersma, editors, Introduction to Marine Micropaleontology, page 151
   For fans of the undersea sci-fi classic The Abyss, a pteropod seems a likely inspiration for the ethereal alien creatures that were the saviors at the film's end. The muscular foot that most snails use for locomotion has been modified in the pteropods into delicate fins for swimming. 2011, Ellen Prager, Sex, Drugs, and Sea Slime: The Oceans' Oddest Creatures and Why They Matter, page 33
   Pteropods, or sea butterflies, have a foot that is modified to form a pair of winglike structures that animals use to propel themselves through the water column. 2013, George Karleskint, Jr, Richard Turner, James Small, Jr, Introduction to Marine Biology, 4th edition, Cengage Learning, page 446