Nudibranchia

Nudibranchia, commonly known as nudibranchs or sea slugs, are a diverse group of marine gastropod mollusks that have lost their shells in adulthood. They inhabit oceans worldwide, from shallow tidal pools to deep waters, and display a wide range of shapes, sizes, and vivid color patterns that often serve as camouflage or warning.

Anatomy and classification: Nudibranchs possess exposed gills and a pair of sensory rhinophores on the head, which detect chemicals in the water. They are traditionally divided into two informal groups: dorids, which bear a circle of gills on the posterior dorsal surface, and aeolids, which carry numerous cerata along the back that can house extensions of the digestive tract. Some aeolids can store defensive nematocysts from cnidarian prey in their cerata, a process known as kleptocnidae.

Diet and ecology: Their diets are varied and specialized, including sponges, hydroids, bryozoans, corals, tunicates, and sometimes other sea slugs. Many species exhibit chemical defenses derived from prey, and some also employ aposematic coloration to deter predators.

Life cycle and reproduction: Nudibranchs are hermaphrodites and typically engage in reciprocal mating, exchanging sperm before laying eggs in gelatinous ribbons or masses. The eggs hatch into free-swimming larval forms, typically veligers, which undergo metamorphosis into the shell-less adults.

Taxonomy and study: Nudibranchia is a major lineage within the class Gastropoda. They are notable for their ecological roles as predators and for their remarkable diversity, which continues to be expanded by ongoing descriptions of new species.