Elysia viridis is a sacoglossan sea slug of the family Plakobranchidae[1][2]. They are occasionally nicknamed the sap sucking slugs for their ability to suck the cytoplasm out of the algae they prey upon, [1][2]. Adult length is considered to be between 15-20 mm long[3][2], and they vary in color from greens to brownish hues[2]. Elysia viridis is one of few organisms capable of kleptoplasty; when consuming the cytoplasm of its algal prey E. viridis can retain the chloroplasts in working condition, and being able to benefit from their continued photosynthesis[4][5][6].
Adult length of E. viridis ranges between 15-20mm[2][3], with an healthy adult weight of 15-20 mg[1][4]. The surface of the slug is covered in tiny spots of red, yellow, blue or green that are reported to have a glistening appearance[2]. Parapodia extend from the sides of the slug, and are the main location of captured chloroplasts. Rhinophores extend upward from its head[2][4]. Elysia viridis feed using radular teeth, which in this species, E. gordanae, can vary in design based upon the diet of the individual[2].
Distribution
Elysia viridis is located in the Northeastern Atlantic, primarily around the British Islands, but has been found further north in Sweden and Norway[1][6], as well as in the Mediterranean Sea[1][2][7]. A report of E. viridis being found in south Africa was published in 1987[8], but the identification that specimen was later changed to Elysia sp. by the same author[9][7]. Elysia viridis occurs in the intertidal zone typically submerged on its algal prey between 1 and 5 meters below the surface[1].
Ecology
Elysia viridis on algae
Elysia viridis feed on algae, primarily of the genus Codium, with a noted favorability towards C. fragile, C. sericea, and C. rupestris[1][5]. E. viridis has been found to be less selective of algal hosts than other members of Elysia[1][10]. E. viridis deposit coiled egg masses onto the thallus of its prey, or on nearby underwater surfaces, that hatch into a larval stage called a veliger[3][10][11]. Veliger are planktotrophic and consume free floating unicellular algae[3][11]. Once the propodeum develops on the larvae they search for a macroalgal host, contact with which appears to trigger a metamorphosis into the adult form, but the trigger for this metamorphosis is unconfirmed[3][11].
Kleptoplasty
Elysia viridis is most notable for its capability of performing kleptoplasty, and maintaining a subcellular endosymbiotic relationship with chloroplasts derived from the algae in the genus Codium, most often C. fragile[4][10][12]. When consuming the cytoplasm of the algae, E. viridis is able to retain the chloroplasts in a functional state; chloroplasts are phagocytized, while digesting the other cytoplasmic contents are digested[4][5][10]. The captured chloroplasts (kleptoplasts) retain their ability to photosynthesize, the photosynthates of which can benefit the slug nutritionally[4][10][13]. Kleptoplasts can also be broken down and used as a pre-stored energy source in situations where the slug is deprived of food sources and light[4].
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