Malacobdellidae is a monogeneric family within the phylum Nemertea. It is included with the order Hoplonemertea within the class Enopla (formerly in monotypic order Bdellonemertea of the same class).[1]
The family, as well as its sole genus Malacobdella, is characterized by a posterior ventral sucker and a proboscis lacking a stylet.[2] As in other Hoplonemertea, the lateral longitudinal nerve cord is located internal to the body wall muscles, in the mesenchyme.[3]
Members of Bdellonemertea are all commensal, living in the mantle cavities of bivalves.[4] The only non-marine and non-bivalve hosted species, Malacobdella auriculae, is doubtful. It was described in 1847 by Émile Blanchard on the basis of a single drawing of his colleague and probably wasn't even a nemertean.[5] Malacobdella feed on small food particles that are brought into the mollusk's ctenidia.