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 (marine gastropod mollusks ) 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 .
14-487: See text Lower Heterobranchia , also known as the Allogastropoda , is a group of rather specialized, highly evolved sea slugs and sea snails , ( marine gastropod mollusks ) within the subclass Heterobranchia . Although the great majority of Lower Heterobranchs are indeed marine, a few have succeeded in making the transition to freshwater . The shell shapes in this group are typically those that are seen in
28-510: A pallial lung instead of a gill , or gills. The group includes many land and freshwater families, and several marine families. The taxon Pulmonata as traditionally defined was found to be polyphyletic in a molecular study per Jörger et al. , dating from 2010. Pulmonata are known from the Carboniferous period to the present. Pulmonates have a single atrium and kidney, and a concentrated symmetrical nervous system. The mantle cavity
42-604: A contrasting color, which act as gills. All species of genuine sea slugs have a selected prey animal on which they depend for food, including certain jellyfish , bryozoans , sea anemones , plankton , and other species of sea slugs. Sea slugs have brains. For example, Aplysia californica has a brain of about 20,000 nerve cells. The name "sea slug" is often applied to numerous different evolutionary lineages of marine gastropod molluscs or sea snails , specifically those gastropods that are either not conchiferous (shell-bearing) or appear not to be. In evolutionary terms, losing
56-444: A foul ink or secrete a viscous slime to deter predators. Some species of acochlidian sea slugs have made evolutionary transitions to living in freshwater streams and there is at least one evolutionary transition to land. Pulmonata Pulmonata or pulmonates is an informal group (previously an order , and before that, a subclass ) of snails and slugs characterized by the ability to breathe air, by virtue of having
70-479: A process in which the slug absorbs chloroplasts from the algae it eats, and uses "stolen" cells to photosynthesize sugars. The ruffles of the lettuce sea slug increase the slug's surface area, allowing the cells to absorb more light. Headshield slugs, like the Chelidonura varians , use their shovel-shaped heads to dig into the sand, where they spend most of their time. The shield also protects sand from entering
84-615: Is on the right side of the body, and lacks gills, instead being converted into a vascularised lung. Most species have a shell, but no operculum , although the group does also include several shell-less slugs. Pulmonates are hermaphroditic , and some groups possess love darts . The taxonomy of this group according to the taxonomy of the Gastropoda (Ponder & Lindberg, 1997) was as follows: Order Pulmonata Cuvier in Blainville, 1814 - pulmonates The taxonomy of this group according to
98-415: The taxonomy of the Gastropoda (Bouchet & Rocroi, 2005) was as follows: Contains the informal group Basommatophora and the clade Eupulmonata Contains the clade Hygrophila Contains the clades Systellommatophora and Stylommatophora Contains the subclades Elasmognatha , Orthurethra and the informal group Sigmurethra Two superfamilies belongs to clade Sigmurethra, but they are not in
112-717: The Heterobranchia : they moved Glacidorboidea and Pyramidelloidea to Panpulmonata . Wägele et al. (2014): moved Rissoelloidea and Acteonoidea from Lower Heterobranchia to Euthyneura . Kano et al. (2016): moved Ringiculoidea from Lower Heterobranchia to Euthyneura . So the following taxa remain within the Lower Heterobranchia: Sea slug Sea slugs have an enormous variation in body shape, color, and size. Most are partially translucent. The often bright colors of reef -dwelling species imply that these animals are under constant threat of predators. Still,
126-412: The color can warn other animals of the sea slug's toxic stinging cells ( nematocysts ) or offensive taste. Like all gastropods , they have small, razor-sharp teeth called radulas . Most sea slugs have a pair of rhinophores —sensory tentacles used primarily for the sense of smell—on their head, with a small eye at the base of each rhinophore. Many have feathery structures ( cerata ) on the back, often in
140-632: The informal taxonomic group Opisthobranchia : There is also one group of "sea slugs" within the informal group Pulmonata : Like many nudibranchs, Glaucus atlanticus can store and use stinging cells, or nematocysts , from its prey ( Portuguese man o' war ) in its finger-like cerata . Other species, like the Pyjama slug Chromodoris quadricolor , may use their striking colors to advertise their foul chemical taste. The lettuce sea slug ( Elysia crispata ) has lettuce-like ruffles that line its body. This slug, like other Sacoglossa , uses kleptoplasty ,
154-499: The mantle during burrowing. Peronia indica is a species of air-breathing sea slug, a shell-less marine pulmonate gastropod mollusk in the family Onchidiidae . The largest species of sea hare, the California black sea hare, Aplysia vaccaria can reach a length of 75 centimetres (30 in) and a weight of 14 kilograms (31 lb). Most sea hares have several defenses; in addition to being naturally toxic, they can eject
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#1732852640882168-409: The most familiar sort of sea slug. Although most nudibranchs are not large, they are often very eye-catching because so many species have brilliant coloration. In addition to nudibranchs, a number of other taxa of marine gastropods (some easily mistaken for nudibranchs) are also often called "sea slugs". Within the various groups of gastropods that are called "sea slugs", numerous families are within
182-450: The shell altogether, having a small internal shell, or having a shell so small that the soft parts of the animal cannot retract into it, are all features that have evolved many times independently within the class Gastropoda, on land and in the sea; these features often cause a gastropod to be labeled with the common name "slug". Nudibranchs (clade Nudibranchia ) are a large group of marine gastropods that have no shell at all. These may be
196-580: The sundial, pyramid, rissoella and orbitestellid families of snails. In the taxonomy of the Gastropoda by Bouchet & Rocroi, 2005 , the Lower Heterobranchia is an Informal Group. Superfamilies within the Lower Heterobranchia include: (Taxa that are exclusively fossil are indicated with a dagger †) For a more detailed taxonomy see: Taxonomy of the Gastropoda (Bouchet & Rocroi, 2005)#Informal group "Lower Heterobranchia" (= Allogastropoda) Jörger et al. (2010) have redefined major groups within
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