An order of the class Enopla in the phylum Rhynchocoela. The proboscis is unarmed. The alimentary system comprises the mouth, papillate foregut, sinuous intestine without diverticula, and anus. Members are characterized by the presence of a posterior adhesive disk and dorsoventral flattening of the body, which lacks eyes, cephalic slits, and cerebral organs. The order contains the single genus Malacobdella, with three species ectocommensal in the mantle cavity of marine bivalves and one in the pulmonary sac of a fresh-water gastropod. Malacobdella grossa, in the bivalve Zirfaea crispata, abstracts particulate food such as planktonic organisms from the host's feeding current, collects these by a unique filtration system, and digests them in the intestine by a combination of extracellular and intracellular processes. Carbohydrases predominate in the digestive physiology, in contrast to other, carnivorous rhynchocoelans, where proteases are dominant.