Sea slug is a common name for some marine invertebrates with varying levels of resemblance to terrestrial slugs. Most creatures known as sea slugs are gastropods, i.e. they are sea snails that, over evolutionary time, have either entirely lost their shells or have seemingly lost their shells due to having a significantly reduced or internal shell. The name "sea slug" is often applied to nudibranchs and a paraphyletic set of other marine gastropods without apparent shells.
Aplysiidae is the only family in the superfamily Aplysioidea, within the clade Anaspidea. These animals are commonly called sea hares because, unlike most sea slugs, they are often quite large, and when they are underwater, their rounded body shape and the long rhinophores on their heads mean that their overall shape resembles that of a sitting rabbit or hare. Sea hares are however sea snails with shells reduced to a small plate hidden between the parapodia, and some species are extremely large. The Californian black sea hare, Aplysia vaccaria is arguably the largest living gastropod species, and is certainly the largest living heterobranch gastropod.
Bursatella leachii, whose common name is the ragged sea hare or shaggy sea hare, is a species of large sea slug: a marine gastropod mollusk in the sea hare family Aplysiidae. It has an almost pantropical distribution, from the Mediterranean to the Caribbean, but excluding the central and eastern Pacific Ocean. Its long planktonic larval period and short life cycle make able to colonise new areas and increase dramatically in number if food supplies are favourable.
Notarchus is a genus of sea slugs or sea hares, marine opisthobranch gastropod mollusks in the family Aplysiidae, the sea hares.
Petalifera is a genus of sea slugs or sea hares, marine gastropod mollusks belonging to the family Aplysiidae, the sea hares.
Aplysia is a genus of medium-sized to extremely large sea slugs, specifically sea hares, which are a kind of marine gastropod mollusk.
Stylocheilus is a genus of sea slugs, specifically sea hares, marine opisthobranch gastropod mollusks in the family Aplysiidae, the sea hares.
Syphonota geographica, or the geographic sea hare, is a species of sea slug or sea hare, a marine opisthobranch gastropod mollusk in the family Aplysiidae, the sea hares.
The Notobranchaeidae, or "naked sea butterflies", are a taxonomic family of floating sea slugs, specifically under the subclass Opistobranchia, also called "sea angels".
The Pneumodermatidae are a family of sea angels, or small floating predatory sea snails or sea slugs. They are pelagic marine heterobranch opisthobranch gastropod mollusks in the clade Gymnosomata.
Acteonidae, common name the "barrel bubble snails", is a family of small sea snails, marine gastropod mollusks of the informal group Lower Heterobranchia.
Akera is a marine genus of sea hare in the family Akeridae, known from the late Callovian (Jurassic) to the recent periods.
Diaphanidae is a taxonomic family of small sea snails, marine opisthobranch gastropod molluscs or micromollusks in the superfamily Diaphanoidea, the headshield slugs and bubble snails.
Atys is a genus of very small to medium-sized sea snails, marine opisthobranch gastropod mollusks in the family Haminoeidae.
Tenellia adspersa, common name the miniature aeolis, is a species of very small sea slug, an aeolid nudibranch, a marine gastropod mollusk in the family Fionidae. It is the type species of the genus Tenellia.
Phyllaplysia taylori, synonym Phyllaplysia zostericola, common names the "eelgrass sea hare" and "Taylor's sea hare", is a species of sea slug, specifically a sea hare, a marine gastropod mollusk in the family Aplysiidae, the sea hares.
The family Cavoliniidae is a taxonomic group of small floating sea snails, pelagic marine opisthobranch gastropod mollusks.
Haminoea is a genus of medium-sized sea snails or bubble snails, marine opisthobranch gastropod molluscs in the family Haminoeidae, the haminoea bubble snails, part of the clade Cephalaspidea, the headshield slugs and bubble snails.
Berghia coerulescens is a species of sea slug, a marine nudibranch in the family Aeolidiidae. It is the type species of the genus Berghia.
Berthella stellata is a species of sea slug in the family Pleurobranchidae. It is found in shallow water in the Mediterranean Sea, the western Atlantic Ocean and the tropical and subtropical Indo-Pacific region.
