Plakobranchidae Family of Sea Slugs

One Sea Slug of the Plakobranchidae Family can be found in this website:

Mexican Dancer, Elysia diomedia. A representative of the Plakobranchidae Family of Sea Slugs.

Phylogeny: Plakobranchid Sea Slugs of the Plakobranchidae Family  are in the phylum Mollusca and the class Gastropoda. They are in the subclass Heterobranchia, the infraclass Euthyneura, the subterclass Tectipleura, the superorder Sacoglossa, and the superfamily Plakobranchoidea. The Plakobranchidae Family is one of five families in this superfamily. The Plakobranchidae Family contains four genera and one hundred thirty-five species. Species in this family are also commonly known as Plakobranchids, Solar Sea Slugs, Sacoglossans, and “sap-sucking slugs”. The name Plakobranchidae comes from the Greek words meaning “flat, broad, or table-like gills”. This refers to the dorsal surface and lateral parapodia on these animals.

Morphology: Plakobranchid Sea Slugs, like other gastropods, have a shell and operculum for a portion of their lives. After their larval phase they are shell-less. They often resemble nudibranchs, in that they have folds on their backs, however, they are not closely related to nudibranchs They have fairly flattened bodies, with no dorsal papillae. Their parapodium (lateral foot extension) extends broadly in 2 layers or flaps. Most Plakobranchids have a form of tentacles on their head that resemble ears. Oral tentacles may be small or absent and their foot is elongated. They have a bilaterally symmetrical nervous system. Many species in the Family are green in color, from the chloroplasts in their diet. Most species are less than 4 cm (1.5 inches) in length but some will attain twice that size.

Habitat and Distribution: Plakobranchids are generally found on hard substrates or on their host plants in shallow water at depths up to 30 m (100 feet). They are found are found worldwide in temperate to tropical seas. At least seven species from this family are found in Mexican waters.

Reproduction:  Plakobranchids are simultaneous hermaphrodites (having both male and female reproductive organs). Reproduction is sexual with internal fertilization. The fertilized eggs are laid, by the thousands, in a flat spiral  ribbon. The eggs hatch into veliger larva and remain in a planktonic state for some time before metamorphosing into their benthic adult state.

Ecosystem Interactions: Plakobranchids are also known as “sap-sucking slugs”. They get this name from their practice of piercing the cells of marine plants and sucking out the juices. In doing so, they ingest functional chloroplasts which they retain which continues to photosynthesize and provide sugars for the slug’s nutrition. This use of sunlight, which they are dependent upon for survival, to obtain energy gives rise to the name “Solar Sea Slugs.” Many Plakobranchids reside on the algae that they eat and are camouflaged to match their host. This puts them in harms way as they may be accidentally eaten by other herbivores. They have the ability to incorporate chemical deterrents found in their host plants that are an aide to avoid predation. They are preyed upon by crustaceans, fish, nemerteans and other mollusks.