''Elysia crispata'',

common name In biology, a common name of a taxon or organism (also known as a vernacular name, English name, colloquial name, country name, popular name, or farmer's name) is a name that is based on the normal language of everyday life; and is often con ...

the lettuce sea slug or lettuce slug, is a large and colorful

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), ...

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

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 ...

. The lettuce slug resembles a

nudibranch Nudibranchs () are a group of soft-bodied marine gastropod molluscs, belonging to the order Nudibranchia, that shed their shells after their larval stage. They are noted for their often extraordinary colours and striking forms, and they have b ...

, but it is not closely related to that clade of gastropods; it is classified as a

sacoglossan 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 ...

Description

This species is called the lettuce slug because it is often green in color, and it always has a very frilly edge to its

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 ...

. This makes the slug resemble the curly kinds of

lettuce Lettuce (''Lactuca sativa'') is an annual plant of the family Asteraceae mostly grown as a leaf vegetable. The leaves are most often used raw in Green salad, green salads, although lettuce is also seen in other kinds of food, such as sandwiche ...

, such as the

lollo rosso Lettuce (''Lactuca sativa'') is an annual plant of the family Asteraceae mostly grown as a leaf vegetable. The leaves are most often used raw in green salads, although lettuce is also seen in other kinds of food, such as sandwiches, wraps and ...

variety. The maximum length of this species is about 5 cm and 3 cm in width. The lettuce slug is extremely variable in color: it can also be blue, or very pale with red lines or yellow lines.

Distribution

This species lives in the tropical parts of the western Atlantic, and the Caribbean faunal zone. They are found in more coastal and tropical reef areas where the water is shallow and clear.

Diet

''E. crispata'' can be either heterotrophic or autotrophic throughout their lifespan. As juveniles, food is consumed and digested quickly, with little chloroplast retention. Upon reaching maturity, kleptoplasty becomes an important energy source. The primary food source of ''E. crispata'' is relatively unknown, although some individuals have been known to consume a diversity of algal species such as ''

Vaucheria litorea ''Vaucheria litorea'' is a species of yellow-green algae (Xanthophyceae). It grows in a filamentous fashion (forming long tubular cells connected end to end). ''V. litorea'' is a common intertidal species of coastal brackish waters and salt mar ...

Caulerpa verticillata ''Caulerpa verticillata'' is a species of seaweed in the ''Caulerpaceae'' family. The seaweed has a green thallus that spreads outward to around forming dense low mats. The species is found in warmer waters of the Indian and Pacific Oceans pa ...

Caulerpa racemosa ''Caulerpa racemosa'' is a species of edible Green algae, green alga, a seaweed in the family Caulerpaceae. It is commonly known as sea grapes (along with the related ''Caulerpa lentillifera'') and is found in many areas of shallow sea around the ...

, Halimeda discoidea, Halimeda incrassate, Halimeda monile,'' and ''Penicillus capitatus; C. verticillata'' being suitable for a limited amount of time. This diversity in food sources is a different characteristic compared to other Sacoglossan’s who are specialized for one species of algae, and gives ''E. crispata'' a survival advantage when food is depleted or sparse. Chloroplasts within their

(fleshy dorsal protrusions) continue to produce energy products through carbon fixation throughout their life and have been found to function efficiently for a little over a month.

Kleptoplasty

Also known as chloroplast symbiosis, kleptoplasty is the energy-providing mechanism that gives the

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’s the nickname, “solar-powered sea slugs”, and ''E. crispata'' the name, “lettuce sea slug.” As algal food is being digested, the chloroplasts are absorbed into the cells lining the digestive tract and up into their parapodia. How many chloroplasts the slug sequesters and the length of retention depends on the individual species of slug. Chloroplast retention in ''E. crispata'' tends to last around 40 days. Given the variation in their diet, chloroplasts from different algal species have been found to be taken up into the same cells, functioning normally alongside the other. ''E. crispata'' is closely related to ''E. chlorotica'', both having a long-term chloroplast retention ability, where other species within the same genus tend to have more short-term retention. This ability makes it possible to withstand long periods of time without food. In the absence of food, ''E. crispata'' will invest energy trying to find food rather than slowing down and conserving energy. Although it hasn’t been exclusively studied for this organism, one possibility of the mechanism behind long-term retention is due to the amount of extracellular components which prolong chloroplast activity, depending on the species of algae eaten. As ''E. crispata'' continues to consume food, the chloroplasts ingested will continuously replace older chloroplasts while food is available. Their long-term retention is an evolutionary adaption which allows a greater chance of survival during drastic environmental changes.

Reproduction

Very little is known of the mating behaviors of ''E. crispata''. Typically the egg mass is laid on flat, upright algae, and embryo development takes about 15 days. Eggs are very small, between 106–113 micrometres, and eggs vary in average size by location. Elysia Crispata Reproduction

Newly hatched ''E. crispata'' demonstrate a dispersal dimorphism, not to be confused with poecilogony. Babies can either undergo intracapsular metamorphosis, or post-hatching metamorphosis, giving ''E. crispata'' variation in their dispersal strategy. This allows some clutches to remain stationary to that habitat, or allowing them to swim to a new habitat before metamorphosing. Some species of Sacoglossan such as ''Elysia tuca'', invest extra energy to create extra-cellular yolk which is weaved into their egg mass, providing a greater abundance of nutrients for larval growth, which in turn produces larger progeny. ''E. crispata'', however, does not produce extra-cellular yolk, which affects the size of the eggs.

References

External links

* Rosenberg, G., F. Moretzsohn, and E. F. García. 2009. ''Gastropoda (Mollusca) of the Gulf of Mexico'', Pp. 579–699 in Felder, D.L. and D.K. Camp (eds.), Gulf of Mexico–Origins, Waters, and Biota. Biodiversity. Texas A&M Press, College Station, Texas. * * * {{taxonbar, from=Q1410691 Plakobranchidae Molluscs of the Atlantic Ocean Gastropods described in 1863 Taxa named by Otto Andreas Lowson Mörch