dimyaria

from The Century Dictionary.

• A general name for those bivalves whose shells are closed by two adductor muscles, distinct and widely removed from each other, as in the mussel or clam.
• A group or branch of Nemertini in which the dermal musculature consists of an external coat of circular muscles and an internal coat of longitudinal muscles. It includes the anoplous forms belonging to the orders Protonemertini, Mesonemertini, and Metanemertini. Contrasted with *Trimyaria.