Saltwater Aquarium Guide -- Sea Slugs & Nudibranchs

Sea Slugs & Nudibranchs:

Sea Slugs belong to the diverse sub class Optisthobranchia with over 13,000 species. Of primary interest to the aquarium hobbyist are the families Aplysidae (Sea Hares), Elysiidae (Lettuce Sea Slug), Chromodorididae (Nudibranch), Polyceridae (Nudibranch), Hexabranchidae (Spanish Dancer), and Phyllidiidae (Worty Nudibranch).

All of these organisms display vivid colors and an unusual body shape. Typically found in tropical reefs, Sea Slugs normally lack a shell. If they do have a shell, it is completely covered by the mantle or body tissue. The most notable characteristic is the pair of stalked rhinophores or horns at the head of the Slug. These contain cilia used to detect motion and chemical smells. On some species, they can be withdrawn into the body if threatened. The Sea Slug also has external gills that are located at the rear or middle back. A few species will lose these as they mature, and others have secondary posterior gills that can be extended.

Most Sea Slugs will use toxins or nematocysts as their primary defense mechanism. Their bright colors also send the signal, "I am poisonous, leave me alone." The Sea Hare can secrete a purple cloud to escape predators. In reef aquariums, some care must be taken as some Crabs, Starfish, and Anemones will prey on Sea Slugs. Sea Slugs can be either carnivorous or herbivorous, but they are usually very selective in what they eat. Some Sea Slugs will eat the Aiptasia Anemone that plagues some reef aquariums, and others will consume hair algae. Some Sea Slugs have such selective appetites, they are almost impossible to maintain in an aquarium setting.

Most nudibranchs eat a specific species of sponge or bryozoans and will accept no substitutes. Because of this, only experts who have had considerable experience with and knowledge of Nudibranchs should attempt to maintain them.

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