What is Sea slug?
{{Taxobox | image = Nembrotha_kubaryana.jpg | image_caption =''Nembrotha kubaryana'' <br/>feeding on [[tunicate]]s | regnum = [[Animal]]ia | phylum = [[Mollusca]] | classis = [[Gastropoda]] | unranked_superfamilia = clade [[Heterobranchia]]}} [[File:Glossodoris atromarginata.jpg|thumb|right| The nudibranch ''Glossodoris atromarginata'']] '''Sea slug''' is an informal name for a group of [[gastropods]] which look similar, but are not [[monophyletic]]. They are [[polyphyletic]]. Their similar shape and life styles is an example of [[convergent evolution]]. The group includes: *[[Heterobranchia]] **[[Nudibranch]]s: a [[clade]] with [[bilateral symmetry]] **Sacoglossa, a clade of Heterobranch sea slugs and snails which go in for ''kleptoplasty'' ('stealing' [[plastid]]s). They eat algae and keep the [[chloroplast]]s for their own use. **[[Opisthobranch]]s: a long-used term now just an informal label. ***Sea angels, or [[clione]]s, are opisthobranch gastropod molluscs of the clade Gymnosomata. ***Sea hares are medium to large size marine gastropod molluscs. They belong to two families of the Opisthobranchia. ***Cephalaspidea: a sub-order of Opisthobranch gastropod molluscs. They usually have a reduced internal shell. *Onchidiidae: a family of air-breathing sea slugs. **Sea butterflies: a group of [[pelagic]] sea snails sometimes called [[pteropod]]s. They belong to the clade Thecosomata. It would seem that their similar growth pattern, with the loss of [[torsion]], [[bilateral symmetry]], reduction of the Gastropod [[Animal shell|shell]], and somewhat similar life styles, evolved a number of times in the Gastropods. [[Category:Gastropods]]