The lettuce sea slug is a species of soft-bodied marine mollusk deriving its name from the frilly, densely folded edges of its body that make it look like curly-leafed lettuce varieties. Found mostly in the tropical regions of the Atlantic Ocean and some parts of the Caribbean, these slugs prefer reef areas and clear shallow waters that are not deeper than 12 m and where the currents are mild.
These frilly marine creatures are quite small, reaching only 3-5 cm in width in adulthood. They are also varied in terms of coloring – green is the most widespread color, but blue and cream-colored individuals are also common. Some lettuce slugs are uniform in color, while others have red, yellow or orange stripes, the hues and patterns depending on the environment they want to blend into. The other conspicuous physical feature of lettuce slugs is the existence of two horns on the head of the animal. Lettuce slugs are slow-moving animals, advancing either by contracting their muscles or with the help of the small hairs found on the bottom of the body.
Lettuce slugs are often called solar-powered creatures because one of the methods they use to obtain nutrients is kleptoplasty, the process of extracting and sequestering chloroplasts, the cells that carry out photosynthesis in the algae. Being able to incorporate chloroplasts for around 40 days, the lettuce slug becomes able to photosynthesize in an indirect way, which helps it survive even when the algae that the slug would otherwise consume become scarce.
Very little is known about the proliferation of lettuce slugs, but they seem to be hermaphroditic, having a hermaphroditic duct which leads to an ovotestis. Fertilization occurs by one individual inserting its penis-like organ into the female pore of the other individual. Lettuce slugs lay large quantities of small eggs, usually between 30 and 500 eggs at a time, measuring 106-113 micrometers each and placed on suitably flat surfaces. The eggs hatch into larvae after around 15 days. The larvae metamorphose into tiny slugs in less than a week. Juveniles are sessile in the larvae phase, to be able to benefit more from the sun’s rays, but the adult lettuce sea slug is quite mobile, moving around its territory quite a lot.