Sea slug

Sea slugs are a group of marine gastropod mollusks that have evolved to lose their shells, or have internalized or reduced shells, in the adult stage. They are a diverse and colorful group belonging to several different taxonomic lineages within the Opisthobranchia, a subclass of gastropods. This subclass also includes bubble snails, side-gill slugs, and sea hares.

Unlike their shelled snail relatives, sea slugs have adapted various defense mechanisms against predators, including camouflage, bright coloration (aposematism) to advertise toxicity, and the ability to sequester stinging cells (nematocysts) from consumed cnidarians like jellyfish and anemones for their own defense. Some species can also synthesize noxious chemicals or discharge clouds of ink or mucus.

Sea slugs exhibit a wide range of body forms and feeding habits. Some are herbivores, grazing on algae, while others are carnivores, preying on sponges, hydroids, bryozoans, other sea slugs, or even small fish. Nudibranchs, a well-known group of sea slugs, are particularly noted for their elaborate cerata, fleshy dorsal appendages that serve as both respiratory organs and defensive structures.

Sea slugs are found in marine environments worldwide, from shallow intertidal zones to deep-sea habitats. Their sensitivity to environmental changes makes them useful indicators of marine ecosystem health. The study of sea slugs provides valuable insights into evolutionary biology, chemical ecology, and marine biodiversity.