The Collaborative International Dictionary of English v.0.48:

Monomya \Mo*no"my*a\, Monomyaria \Mon`o*my*a"ri*a\, n. pl. [NL.,
   fr. Gr. mo`nos single + ?, ?, muscle.] (Zool.)
   An order of lamellibranchs having but one muscle for closing
   the shell, as the oyster.
   [1913 Webster] Monomyarian