Lettuce sea slug

Elysia crispata

''Elysia crispata'', common name the lettuce sea slug, is a large and colorful species of sea slug, a marine gastropod mollusk. The lettuce slug resembles a nudibranch, but it is not closely related to that clade of gastropods; it is classified as a sacoglossan.
Lettuce Sea Slug Sep14, 2017. Dive site The Sampler, in Klein Bonaire.
Thanks to an overprotective dive guide I was not able to get a better pic of this beauty but you can see the slug is iridescent blue. These beautiful slugs are usually brilliantly coloured and this in itself can act as a deterrent against predators. Some sea slugs secrete acid from stinging cells in their tentacles while others secrete acid from cells in their mantle.
Nudibranchs are slow moving, can swim or be propelled along either by muscular contraction or by millions of tiny hairs on the bottom of a fleshy 'foot', they have a voracious appetite and feed with a rasp like tongue.
Nudibranch lay their eggs in a ribbon effect on the sand, in different colours depending on species. 
http://www.whatsthatfish.com/fish/lettuce-sea-slug/1581  Caribbean Netherlands,Elysia crispata,Geotagged,Lettuce sea slug,Summer

Appearance

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. This makes the slug resemble the curly kinds of lettuce, such as the lollo rosso 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.

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. 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.

Food

''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, Caulerpa verticillata, Caulerpa racemosa, Halimeda discoidea, Halimeda incrassate, Halimeda monile,'' and ''Penicillus capitatus; C. verticillata'' being suitable for a limited amount of time....hieroglyph snipped... 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 parapodia continue to produce energy products through carbon fixation throughout their life and have been found to function efficiently for a little over a month.

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Taxonomy
KingdomAnimalia
DivisionMollusca
ClassGastropoda
OrderSacoglossa
FamilyPlakobranchidae
GenusElysia
SpeciesE. crispata