Madrellids are often mistaken for aeolids but they are anatomically closer to the Arminidae. Their shape is elongate which tapers to a pointed tail and a broad mantle with a distinct brim. They possess cerata on the dorsum that are long, containing branches of the digestive gland and have a globose distal end. These are arranged as a fringe all around the body including the anterior margin of the head (never seen in aeolids) and are capable of independent movement. This can give them the appearance of a sea anemone at times. Cnidosacs are absent, but glands producing a vivid yellow or orange fluid when an animal is disturbed, are present at the base of the cerata and over the whole body surface. The cerata can be cast off when the animal is distressed. There is a large oral veil. The rhinophores are non-retractile and are characteristic, each being well differentiated between stalk and club, the club being covered with many papillae. They lack a caruncle between the rhinophores, a feature that assists in distinguishing them from the related Janolidae. Madrellids feed upon encrusting bryozoans.