Resilifer

A resilifer is a part of the shell of certain bivalve mollusks. It is either a recess (a pit or groove of some sort) or a process, the function of which is the attachment of an internal ligament, which holds the two valves together.

Hinge area in one valve of an oyster shell (Ostreidae), showing the groove that is the resilifer

An internal ligament (which requires a resilifer to function) is part of the hinge mechanism in certain taxonomic families of bivalve shells, such as oysters and scallops.^[1][2][3] A resilifer (and its associated ligament) is the primary structure comprising the type of bivalve hinge that is known as an "isodont" hinge.

The hinge area in one valve of a scallop shell (Pectinidae), showing the internal ligament still positioned in the resilifer