(spread across the back) instead of the branchial plume. The cerata function in place of gills and facilitate gas exchange through the epidermis. Additionally, aeolids possess a branched digestive gland, which may extend into the cerate and often has tips that contain cnidosacs (stinging cells absorbed from prey species and then used by the nudibranch). They lack a mantle. Some are hosts to zooxanthellae.

The exact systematics of nudibranchs are a topic of recent revision. Traditionally, nudibranchs