Acanthodoris pilosa is easy to distinguish from other nudibranch by its rounded, fluffy, soft-textured appearance. It has long, soft, pointed processes (papillae) all over its back, which are usually of a uniform length and colour. Colour is uniformly distributed and varies from white to brown and purplish-brown to charcoal grey. This sea slug usually grows up to 3 cm in length but may exceptionally reach 7 cm. Juveniles may have a speckled appearance. Two horn-like processes (rhinophores) at the front of the animal characteristically bend towards the rear and are much larger than the other processes (papillae). Up to 9 large gills form a circle at the rear of the animal.Feeds on encrusting bryozoans such as Alcyonidium hirsutum and Flustrellidra hispida.