Green Frilly (Lettuce) Slug

Elysia crispata

Identification	Vivid green body with ruffled, lettuce-like parapodia (wing-like flaps) that undulate along both sides. The frilly edges are often tipped in blue, giving it an otherworldly appearance.
Maximum Size	Up to 2 inches (5 cm)
Origin	Caribbean — Florida, Bahamas, Gulf of Mexico
Minimum Tank Size	10 gallons
Reef Compatible	Yes — reef safe; beneficial algae consumer

Behavior

Also called the Lettuce Nudibranch, though it is technically a sacoglossan sea slug rather than a true nudibranch. One of the most popular and recognizable sea slugs in the hobby. Grazes on filamentous green algae and Bryopsis, making it a natural algae control agent. The green color comes from chloroplasts absorbed from algae — it can photosynthesize. Peaceful and slow-moving.

Diet & Feeding

Herbivore. Feeds on filamentous green algae, Bryopsis, and Caulerpa. Once algae is depleted, provide dried seaweed or transfer to a tank with more algae growth. May slowly starve in a pristine reef with no algae.

Cautions

Not a true nudibranch — do not confuse with nudibranchs that require live sponge or coral polyps to survive. Sensitive to copper-based medications. May slowly decline once it exhausts the algae supply — monitor closely.