malacobdella

from The Century Dictionary.

• noun A genus of worms, formerly supposed to be leeches, now considered to be parasitic nemerteans, type of a family Malacobdellidæ. M. grossa is a parasite found in the gills of various mollusks.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Zoöl.) A genus of nemertean worms, parasitic in the gill cavity of clams and other bivalves. They have a large posterior sucker, like that of a leech. See Illust. of bdellomorpha.