The lettuce sea slug is a nudibranch that feeds on higher algae.

Unlike most other sea slugs, which are specilized on a specific target species, they feed on various algae species. Its feed includes such algae as Halimeda, Penicillus and Bryopsis. The latter makes it highly intresting as a potential counter to Bryopsis spreading in the tank. However, Elysia crispata is a slow eater. Ideally it should be placed directly on the algae that you want to rid yourself of.

To feed, Elysia crispata sucks out the juices and tissue from algae. A curious ability is that this family of snails can preserve chloroplast from the algae in their tissue. They stay intact for multiple months, and the lettuce sea slug can use them for photosynthesis. This process is called kleptoplasty, and these nudibranchs have been dubbed "solar-powered sea slugs" due to it.

Elysia crispata grows to about 5-6 cm length and is suitable for tanks of 30 liters and above, as long as it has a good supply of algae.