Calmella cavolini is a small aeolid (sea slug), with a maximum length of 12mm. It has smooth elongate rhinophores, oral tentacles, and angular anterior foot corners. Cerata, with a common stalk each, are arranged in groups. The front 3 ceratal clusters, which are on each side, are oppositely arranged but the posterior 3 ceratal clusters are arranged alternately. The color of digestive gland duct is bright red but the apical cnidosac is white in color. The jaw plates are purplish red and they show through each side of the slug's head as a reddish color spot. It was reported that it feeds on the hydroid, Eudendrium.