Sea Slugs

Sea slugs are soft-bodied, shell-less mollusks with:

• Oral tentacles on the head.
• Sensory tentacles called rhinophores toward the back of the body.
• Various gills, tubercles and club-shaped growths called cerata on the top of the body.

Sea slugs look like graceful, delicately colored garden slugs. They blend in with the color of the surface they are on.

Sea slugs vary in side from one-eighth of an inch to about 1.5 inches long.

What species of sea slugs live in the Bay?

Eight species of sea slugs are found in the Bay. Four are sacoglossans, which are sea slugs that feed on plants, and four are nudibranchs, which are carnivorous sea slugs.

• The cross-bearer sea slug, Hermaea cruciata
• The dusky sea slug, Stiliger fuscatus
• The emerald sea slug, Elysia chlorotica
• The kitty-cat sea slug, Elysia catula
• The limpet nudibranch, Doridella obscura
• The ridged-back nudibranch, Polycerella conyma
• The rough-back nudibranch, Doris verrucosa
• The striped nudibranch, Cratena pilata

Where do sea slugs live?

Sea slugs can be found in various parts of the Bay, on and around reefs, pilings, buoys, hydroids and bay grass meadows.

What do sea slugs eat?

Sea slugs are divided into two basic types, depending on their diet:

• Herbivorous sacoglossans feed on algae and other plants.
• Carnivorous nudibranchs feed on animals, such as hydroids or jellyfish polyps. Each family of nudibranchs tends to eat one or two particular types of food.

How do sea slugs reproduce?

Sea slugs are hermaphrodites, meaning that each has both male and female sex organs. They are able to mate with any individual of the same species.

• Eggs are fertilized and spirals of egg cases are laid.
• Eggs may take five to 50 days to develop into the first larval form, the free-swimming veliger phase.

Other facts about sea slugs:

• Because they lack shells, nudibranchs rely on bright coloration and strong scent to avoid being preyed upon. Some nudibranch species can eat the stinging cells of jellyfish and store them in their cerata. These “adopted” cells become part of the nudibranch's defense system.
• If taken out of water, sea slugs will turn into shapeless lumps. To view their true shape, keep them in water.