cerata

Cerata are dorsal and lateral outgrowths found on many aeolid nudibranchs and some other opisthobranch mollusks. They vary in number, size, and shape, and can be finger-like, clustered, or crestlike along the body. They often extend in terminal whorls or along the dorsum.

Each ceras contains a ramified digestive gland that ends in a gut diverticulum, increasing surface area for digestion and respiration. The cerata resemble gills, serving gas exchange; their surface permeability allows diffusion of oxygen and carbon dioxide. In many species, the cerata are brightly colored and may move with the animal.

Defense is a key function of cerata in aeolids. Many aeolid nudibranchs possess cnidosacs at the tips of cerata that store nematocysts (stinging cells) acquired from their cnidarian prey. When threatened, these nematocysts can be everted for defense. The degree of nematocyst sequestration varies by species and diet.

Cerata are formed from mantle tissue and are connected to the visceral mass. The arrangement and morphology of cerata are often used in the taxonomy and identification of nudibranchs, as they can vary considerably between species.

Ecology-wise, aeolid nudibranchs typically feed on hydroids, anemones, and other soft-bodied cnidarians. By consuming these prey, they not only obtain nutrients but also acquire defensive cnidarian cells that can be stored in the cerata.