Elysia Chlorotica: Characteristics, Taxonomy And Reproduction

Elysia chlorotica  is a species of marine mollusk commonly called “Emerald Green Sea Slug” or simply “Eastern Emerald”. It belongs to the Placobranchidae family, known for their ability to establish an endosymbiosis relationship with an alga ( Vaucheria litorea ) to photosynthesize food.

The E. chlorotica feeds algae, partially digesting it , and maintaining viable the chloroplast , where a phenomenon occurs called kleptoplasty, which allows the body harness autotrophic capacity plastids. 

In this way, it can survive for months without feeding, feeding only on sunlight thanks to the ability to synthesize chlorophyll through chloroplasts incorporated into the cytoplasm of the cells of its body.

This species of slug is located on the littoral coasts of North America, between Florida and Nova Scotia. It was initially described by August Addison Gould in 1870, however, it was in 2010 when researchers from the University of South Florida led by the Ph.D. Sidney K. Pierce, completed research on the molecular biology of the species and its endosymbiotic relationship with the filamentous chromophytic alga V. litorea .

characteristics general

Due to its physiological characteristics, it was believed that it was one of the first members of the animal kingdom to produce chlorophyll, a green pigment present in plants, algae and bacteria, which facilitates the photosynthesis process .

Members of this species resemble a broad, wavy green leaf with a snail head. During their 9-10 month lifespan, they can grow to a length of 2-5 cm.

In its juvenile phase, it has a grayish-brown color with reddish spots, however, as it feeds on the V. litorea algae , it acquires a bright green hue in its adult phase due to the concentration of chloroplasts in its tissues.

In nature, the adult feeds on algae only occasionally, obtaining metabolic energy from the photosynthetic activity of intracellular chloroplasts.

The emerald green slug survives in aquariums for 8-9 months without feeding, only assimilating energy from sunlight, a period of time similar to its life cycle in nature.

The association of endosymbiosis is not inherited from one generation to another, since the plastids have not been located in the eggs of the species. In contrast, chloroplast endosymbiosis is renewed with each new generation of photosynthetic slugs.

Taxonomy

E. chlorotica (Gould, 1870) is a species of opisthobranch mollusk, a species belonging to the genus Elysia, of the family Elysiidae, of the order Sacoglossa, and class Gastropoda (subclass Opisthobranchia).

This species belongs to the phylum Mollusca (super phylum Lophozoa), infra kingdom Protostomia, sub kingdom Bilateria, of the kingdom Animalia.

Habitat

They inhabit tidal and saline marshes, shallow creeks and inlets, and lagoons less than 0.5 m deep on the Atlantic coast of North America.

This species tolerates salinity levels ranging from almost fresh water (<24 milliosmoles -mosm) to brackish water (> 2,422 mosm).

It generally lives near its main food source, the brown alga V. litorea , due to its endosymbiotic relationship. This alga is an autotrophic organism, which obtains its energy through photosynthesis that occurs in its chloroplasts.

The algae is consumed by the sea slug, storing chloroplasts in the cells of its body, mainly in the digestive tract. These organelles continue their photosynthesis process, providing energy to the sea slug.

Reproduction and development

Sea slugs in general are hermaphrodites, however, in this particular species, interbreeding or sexual reproduction with another individual is more common . Eggs surrounded by thick mucosa are placed in long chains, taking about a week to hatch.

Development phases 

The Elysia chlorotica species has two phases during its life cycle. The juvenile phase that begins before starting to feed on the V. litorea alga , and the adult phase. These phases differ according to the morphology and coloration of the slug.

In the juvenile phase, slugs emerge from the egg as Veliger larvae, that is, they have a shell and a ciliated veil that allows them to swim and get food. At this stage they are brown with reddish ventral spots.

Once the consumption of the alga V. litorea begins , it undergoes a process of transformation or metamorphosis, changing its color and morphology. When consuming the algae, the slug E. chlorotica retains the chloroplasts in its specialized digestive tract, initiating the endosymbiosis process, it acquires a bright green color and loses the red spots.

In the adult stage its structure is characteristic, due to the large lateral parapodia on each side of its body that resemble a leaf. This form is suitable both for camouflage and to streamline the photosynthetic process that occurs within your body.

E. chlorotica under natural conditions completes its life cycle at 11 months of age. Adults die en masse after laying the egg chains in the annual spring.

According to recent studies, this may be due to viral expression, not a biological clock. Due to the presence of a virulent DNA in the nucleus of several examined individuals.

Economic importance

At an ecological level, the “Emerald Green” sea slug currently has no impact on the environment, since they are not predators and do not constitute a particular prey for other species. Its activity in the ecosystems where it develops consists of the symbiosis that it develops with the alga V. litorea .

However, due to its ability to survive only by obtaining energy through the photosynthetic process derived from chloroplasts that it stores in the cells of its body, it is a species of high scientific and economic value. 

Discovering the components and processes that this species has in its genome is the key to generating green energy without the direct intervention of plants.

References 

  1. Chan, CX, Vaysberg, P., Price, DC, Pelletreau, KN, Rumpho, ME, & Bhattacharya, D. (2018). Active host response to algal symbionts in the sea slug Elysia chlorotica. Molecular biology and evolution, 35 (7), 1706-1711.
  2. Woman, CV, Andrews, DL, Manhart, JR, Pierce, SK, & Rumpho, ME (1996). Chloroplast genes are expressed during intracellular symbiotic association of Vaucheria litorea plastids with the sea slug Elysia chlorotica. Proceedings of the National Academy of Sciences, 93 (22), 12333-12338.
  3. Rafferty John P. Elysia chlorotica – Sea Slug. Encyclopedia Britannica. Recovered at: britannica.com
  4. Sidney K. Pierce. (2015) Cellular physiology and biochemistry. University of South Florida. College of Arts and Sciences. Recovered at: Biology.usf.edu
  5. Taxonomic Serial No .: 77940 Elysia chlorotica Gould, 1870. ITIS Report. Recovered at: itis.gov

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