Editing Sea slug (section)

===Gastropod groups===
[[File:Lettuce_Sea_Slug_11-03-2006.jpg|thumb|right|The sacoglossan ''[[Elysia crispata]]'']]
[[File:Chelidonura varians.jpg|thumb|right|The cephalaspidean ''[[Chelidonura varians]]'']]
[[File:Aplysia dactylomela 2.jpg|thumb|right|The [[sea hare]] ''[[Aplysia dactylomela]]'', photographed out of water]]
Within the various groups of gastropods that are called "sea slugs", numerous families are within the informal taxonomic group '''[[Opisthobranchia]]'''. The term "sea slug" is perhaps most often applied to [[nudibranch]]s, many of which are brightly patterned and conspicuously ornate. The name "sea slug" is also often applied to the sacoglossans (clade '''[[Sacoglossa]]'''), the so-called sap-sucking or solar-powered sea slugs which are frequently a shade of green.

Another group of main gastropods that are often labeled as "sea slugs" are the various families of headshield slugs and [[bubble snails]] within the clade '''[[Cephalaspidea]]'''. The [[sea hares]], clade '''[[Aplysiomorpha]]''', have a small, flat, [[proteinaceous]] internal shell. The clades '''[[Thecosomata]]''' and '''[[Gymnosomata]]''' are small [[pelagic]] gastropods known as "sea butterflies" and "sea angels". Many species of sea butterflies retain their shells. These are commonly known as "[[pteropods]]" but are also sometimes called sea slugs; especially the Gymnosomata, which have no shell as adults.
[[File:Onchidella celtica 0377.jpg|thumb|right|The marine pulmonate ''[[Onchidella celtica]]'']]

There is also one group of "sea slugs" within the informal group '''[[Pulmonata]]'''. One very unusual group of marine gastropods that are shell-less are the pulmonate (air-breathing) species in the family [[Onchidiidae]], within the clade '''[[Systellommatophora]]'''.<ref name="Fresh">{{cite web |date=2007 |title=How sea slugs fall in love |url=https://freshscience.org/2007/how-sea-slugs-fall-in-love |access-date=2 May 2014 |website=freshscience.org}}</ref>