Elysia Timida
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''Elysia timida'' is a
species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
of
sacoglossa Sacoglossa are a superorder of small sea slugs and sea snails, marine gastropod mollusks that belong to the clade Heterobranchia known as sacoglossans. There are 284 valid species recognized within this superorder. Sacoglossans live by ingestin ...
n
sea slug Sea slug is a common name for some Marine biology, marine invertebrates with varying levels of resemblance to terrestrial Slug, slugs. Most creatures known as sea slugs are gastropods, i.e. they are Sea snail, sea snails (marine gastropod moll ...
, a marine
opisthobranch Opisthobranchs () is a now 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. Euopistho ...
gastropod Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and fro ...
mollusk Mollusca is a phylum of protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000  extant species of molluscs are recognized, making it the second-largest animal phylum after Arthropoda. The ...
. 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 Chemoreceptor, chemosensory club-shaped, rod-shaped or ear-like structures which are the most prominent part of the external head anatomy in sea slugs, Marine (ocean), marine gastropod opisthobranch mollusks suc ...
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; : parapodia) refers to lateral outgrowths or protrusions from the body. Parapodia are predominantly found in annelids, where they are paired, unjointed late ...
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'' 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 east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern Eur ...
, but has also been found in the Atlantic Ocean, off the
Cape Verde Cape Verde or Cabo Verde, officially the Republic of Cabo Verde, is an island country and archipelagic state of West Africa in the central Atlantic Ocean, consisting of ten volcanic islands with a combined land area of about . These islands ...
and
Canary Islands The Canary Islands (; ) or Canaries are an archipelago in the Atlantic Ocean and the southernmost Autonomous communities of Spain, Autonomous Community of Spain. They are located in the northwest of Africa, with the closest point to the cont ...
, and possibly in the
Caribbean Sea The Caribbean Sea is a sea of the Atlantic Ocean, North Atlantic Ocean in the tropics of the Western Hemisphere, located south of the Gulf of Mexico and southwest of the Sargasso Sea. It is bounded by the Greater Antilles to the north from Cuba ...
. 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,'' is a photosynthetic animal that is able to facilitate photosynthesis through a process called incorporation. ''Elysia timida'' feeds on the alga ''
Acetabularia acetabulum ''Acetabularia acetabulum'', mermaid's wine glass, is a species of green alga in the family Polyphysaceae. It is found in the Mediterranean Sea at a depth of one to two metres. Description This alga adheres to the substrate with rhizoids (root- ...
'' in spring and summer, and on '' Padina pavonica'' in autumn. When ''Elysia timida'' feeds on the alga instead of digesting the chloroplast within the alga, it is able to make use of the
chloroplast A chloroplast () is a type of membrane-bound organelle, organelle known as a plastid that conducts photosynthesis mostly in plant cell, plant and algae, algal cells. Chloroplasts have a high concentration of chlorophyll pigments which captur ...
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 process in symbiosis, symbiotic relationships whereby plastids, notably chloroplasts from algae, are sequestered by the host. The word is derived from ''Kleptes'' (κλέπτης) which is Greek language, Greek ...
. The chloroplasts are able to continue
photosynthesis Photosynthesis ( ) is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabo ...
ing in the slug's tissues for about 45 days, allowing the sea slug to harvest energy from the sun, 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 A hermaphrodite () is a sexually reproducing organism that produces both male and female gametes. Animal species in which individuals are either male or female are gonochoric, which is the opposite of hermaphroditic. The individuals of many ...
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 German Zoological Society. The editors-in-chief are Jürge ...
'' 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