[oper.cu.lum] n, pl -la also -lums [NL, fr. L, cover, fr. operire to shut, cover] (1752) 1: a body process or part that suggests a lid: as a: a horny or shelly plate on the posterior dorsal surface of the foot in many gastropod mollusks that closes the shell when the animal is retracted b: the covering of the gills of a fish--see fish illustration
2: a lid or covering flap (as of a moss capsule or a pyxidium in a seed plant)