The appearance of the face of the shell (i.e., the entire lateral side of the valve or shell halve) is important in distinguishing the basic types of shelled larvae or veligers. This character distinguishes those shelled larvae in which the entire lateral side of the valve is only slightly asymmetrical (or clam-shaped) from those in which the entire lateral side of the valve is very asymmetrical or lopsided, as in the typical mussel shape.
