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Elyssia Pusilla are part of Sacoglossa, also known as the solar powered sea slugs. They may be the most common Elysia species. Sacoglossans are marine gastropods that ingest the chloroplast of algae. Some sea slugs in this superorder are able to take the plastids from the algae they eat and incorporate it into their living tissue in a process called kleptoplasty. Sacoglossa has 2 superfamilies under it: Plakobranchidae and Oxynoace. The distinguishing feature between the two superfamilies is having a shell or being able to store chloroplast. Oxynoacea consists of three shelled families, all of whom don’t photosynthesize with the algae they consume. However, they might be able to retain the chloroplast and use it as camouflage. Elysia Pusilla is under the superfamily Plakobranchidae. The majority of the organisms in this superfamily are shell less, however, many develop a shell before hatching. They use the chloroplast they eat and store it in their tissues. Specifically, the algae is digested, but the plasmids are still intact, allowing it to be incorporated into the host organism. Sacoglossa are the only metazoans on earth to exhibit kleptoplasty. The only other organisms known to have this ability are single celled protists. The chloroplast from the algae the organisms feed on are kept alive for weeks to months. Through kleptoplasty, the organisms are able to survive for months just relying on this process.The chloroplast lines the digestive tract, which allows the organisms to survive for several months solely relying on kleptoplasty. Many of the proteins in chloroplast are also encoded in the genome of the sea slugs. The proteins synthesized by the sea slugs are moved into the chloroplast, allowing it to survive for long periods in the host cells. They are typically 1-3 cm in length. The genus Elysia are classified as sea slugs, but can resemble nudibranchs. Elysia pusilla and Elysia stylifera are each other’s closest living relative. They are often found together on a calcareous algae called Halimeda.

Distribution Sacoglossa are found in temperate and tropical oceans, with most of them living in the Central Pacific. Specific species, such as Elysia pusilla are found in the tropical indo pacific ocean, with other species living in the Caribbean.

Description (key characteristics) This uniform green color is due to the ingested chloroplast that is stored in their tissue. They sometimes have white dots as well. Many of the Elysia species have parapodia, wing-like flaps and cephalic tentacles. The parapodia are spread out and flattened to increase surface area for sunlight. Specifically in Elysia pusilla, the parapodia are partially fused. Located on top of its head are white club shaped sensory organs called rhinophores or cephalic tentacles. The rhinophores may be used to detect chemical stimuli which can act as an indicator to metamorphosize. As part of the mollusca family, Elysia pusilla has a soft body. They are also bilaterally symmetrical.

http://www.seaslugforum.net/find/elyspus1 Elysia Pusilla are found exclusively on calcareous green algae, called Halimeda. The shape or texture influences the shape of the nudibranch. When living on broader segments of Halimeda, Elysia tend to be more flattened, while cylindrical segments of Halimeda had more cylindrical shaped Elysia.

Nudibranchs have no gills and breathe through their skin through secondary gills through tentacles looking things, called cerata on their back. In many nudibranchs, the cerata is a blood filled tube that acts as an extension of the digestive system and can be used for defense. In another nudibranch species, such as the aeolids, the cerata contain sacs called cnidosacs that store nematocysts, stinging cells from cnidarians which have been acquired from feeding. The ____ is a plume of gills that circulate the anus.

Add more about the basic description based on being a mollusc, under lophotrochozoans, protostomes and bilateria

Life history// Reproduction The reproduction method poecilogony, an intraspecific reproduction method in which there are two different forms of larvae modes, is quite rare in the animal kingdom. The different egg sizes, or egg dimorphism, are able to produce two kinds of larvae: planktotrophic and lecithotrophic larvae. Lecithotroph, meaning “feeding on yolk” refers to the larvae relying on the yolk sac produced by the mother as they are not able to feed. Planktophic larvae are larvae that must feed on plankton in order to grow and develop. Of the five of the species that have been reported to be capable of this, four of the organisms belong to the order sacoglossans. Elysia Pusilla may be the sixth species and fifth organism in the order sacoglossans to be capable of this. In E. pusilla and E. zuleicae, the planktotrophic larvae are more common, but some still exhibit the lecithotrophic larvae. The smaller size of the lecithotrophic larvae in sacoglossans in comparison to other heterobranchs may allow for developmental plasticity in response to the environment. The frequency of the size difference among the eggs allows sacoglossans to get around the one mode reproductive methods.

Nudibranchs are hermaphrodites and can be simultaneously or sequentially hermaphrodites. To transfer sperm, love darts are stabbed into their partner, with a small piece breaking off (contains the sperm).

Feeding Many nudibranchs are stenophagous, meaning that they only feed on one to two organisms. Specifically, Elysia Pusilla feeds on a green calcareous algae called Halimeda, but can also use the chloroplast and genes from the algae to photosynthesize, thus producing its own energy.