''Elysia timida'' is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

sacoglossa Sacoglossa, commonly known as the sacoglossans or the "solar-powered sea slugs", are a superorder of small sea slugs and sea snails, marine gastropod mollusks that belong to the clade Heterobranchia. Sacoglossans live by ingesting the cellular ...

sea slug 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 t ...

, a marine

opisthobranch Opisthobranchs () is now an informal name for a large and diverse group of specialized complex gastropods which used to be united in the subclass Opisthobranchia. That taxon is no longer considered to represent a monophyletic grouping. Euopisth ...

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

mollusk Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is e ...

. Found in the Mediterranean and nearby parts of the Atlantic, it is herbivorous, feeding on various algae in shallow water.

Description

''Elysia timida'' is a small sea slug, growing to a length of about . The head bears a pair of long, smooth

rhinophore A rhinophore is one of a pair of chemosensory club-shaped, rod-shaped or ear-like structures which are the most prominent part of the external head anatomy in sea slugs, marine gastropod opisthobranch mollusks such as the nudibranchs, sea har ...

s, at the base of which are a pair of black eyespots. The broad foot widens into two lobed

parapodia In invertebrates, the term parapodium ( Gr. ''para'', beyond or beside + ''podia'', feet; plural: parapodia) refers to lateral outgrowths or protrusions from the body. Parapodia are predominantly found in annelids, where they are paired, unjointed ...

which can fold up over the back. The colour is mainly white with widely scattered red or orange spots, but the dorsal surface of the body, and the inner surface of the parapodia, are some shade of mid- to dark green. When the animal has been living in a habitat with ''

Lithophyllum ''Lithophyllum'' is a genus of thalloid red algae belonging to the family Corallinaceae. Fossil record This genus is known in the fossil record from the Silurian to the Quaternary (from about 418.7 to 0.0 million years ago). Fossils of sp ...

'' or other pink calcareous algae, the white colour may be tinged with mauve.

Distribution

This marine species used to be considered endemic to the

Mediterranean Sea The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the ea ...

, but has also been found in the Atlantic Ocean, off the

Cape Verde , national_anthem = () , official_languages = Portuguese , national_languages = Cape Verdean Creole , capital = Praia , coordinates = , largest_city = capital , demonym ...

and

Canary Islands The Canary Islands (; es, Canarias, ), also known informally as the Canaries, are a Spanish autonomous community and archipelago in the Atlantic Ocean, in Macaronesia. At their closest point to the African mainland, they are west of Morocc ...

, and possibly in the

Caribbean Sea The Caribbean Sea ( es, Mar Caribe; french: Mer des Caraïbes; ht, Lanmè Karayib; jam, Kiaribiyan Sii; nl, Caraïbische Zee; pap, Laman Karibe) is a sea of the Atlantic Ocean in the tropics of the Western Hemisphere. It is bounded by Mexico ...

. It is found in sea grass beds and on rocks on which the algae on which it feeds is growing, at depths down to about .

Feeding habits

''Elysia timida'' feeds on the alga '' Acetabularia acetabulum'' in spring and summer, and on ''

Padina pavonica ''Padina pavonica'', commonly known as the peacock's tail, is a small brown alga found in the Indian Ocean, the Pacific Ocean, the Atlantic Ocean and the Mediterranean Sea. It inhabits pools in the littoral zone typically with clayey, silty or sa ...

'' in autumn. It is able to make use of the

chloroplast A chloroplast () is a type of membrane-bound organelle known as a plastid that conducts photosynthesis mostly in plant and algal cells. The photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it in ...

s from the algae, storing them in outgrowths of its digestive gland, where they give the sea slug its green colour. This is called

kleptoplasty Kleptoplasty or kleptoplastidy is a symbiosis, symbiotic phenomenon whereby plastids, notably chloroplasts from algae, are sequestered by host organisms. The word is derived from ''Kleptes'' (κλέπτης) which is Greek language, Greek for thie ...

. The chloroplasts are able to continue photosynthesising in the slug's tissues for about 45 days, and contributing to the slug's nutritional requirements. The slug is able to regulate the process, folding its parapodia over its back to restrict the amount of light the chloroplasts receive, or unfolding its parapodia to allow the chloroplasts full access to the light.

Reproduction

''Elysia timida'' is a

hermaphrodite In reproductive biology, a hermaphrodite () is an organism that has both kinds of reproductive organs and can produce both gametes associated with male and female sexes. Many Taxonomy (biology), taxonomic groups of animals (mostly invertebrate ...

and two individuals come together and mate simultaneously. With their right sides in close proximity, each uses its long penis to insert sperm into the tissues of the other. They then separate and loop round to rearrange themselves, this time depositing sperm into the recipient's genital opening. This second mating phase is sometimes omitted. The eggs are laid in the spring in a white spiral coil about a centimetre across.

References

External links

* Risso A., 1818:
Mémoire sur quelques Gastropodes nouveaux, Nudibranches et Tectibranches observés dans la mer de Nice
'; Journal de Physique, de Chimie, d'Histoire Naturelle et des Arts 87: 368–377. * Gofas, S.; Le Renard, J.; Bouchet, P. (2001). Mollusca. in: Costello, M.J. et al. (Ed.) (2001). ''European register of marine species: a check-list of the marine species in Europe and a bibliography of guides to their identification.'' Collection Patrimoines Naturels. 50: pp. 180–213. * Marin A. & Ros J., 1993: ''Ultrastructural and ecological aspects of the development of chloroplast retention in the Sacoglossan Gastropod Elysia timida''; Journal of Molluscan Studies 59(1): 95–104. . * Schmitt V., et al. (2014)
Chloroplast incorporation and long-term photosynthetic performance through the life cycle in laboratory cultures of ''Elysia timida'' (Sacoglossa, Heterobranchia).
''

Frontiers in Zoology ''Frontiers in Zoology'' is a peer-reviewed open access scientific journal covering all aspects of zoology. It was established in 2004 and is published by BioMed Central on behalf of the . The editors-in-chief are Jürgen Heinze (University of Re ...

'' 11:5. . * {{Taxonbar, from=Q3015747 Plakobranchidae Molluscs of the Atlantic Ocean Molluscs of the Mediterranean Sea Gastropods of Cape Verde Gastropods described in 1818 Taxa named by Antoine Risso