Where Is Umbo Found?

Locate the umbo, the bump at the anterior end of the valve. This is the oldest part of the clam shell. Find the hinge ligament which hinges the valves together and observe the growth rings.

What is the umbo and where is it located?

The umbo is situated above the hinge line. In those bivalves where the umbones do not protrude, as is the case for example in some mussels, the umbones can nonetheless usually be readily identified by examining the concentric growth lines of the shell.

Is the umbo dorsal?

The shell grows comarginally around the post‑larval shell, which remains as a beak somewhere along the dorsal margin. The area surrounding the beak is known as the umbo although some regard these terms as interchangeable. ... The beaks effectively divide the dorsal margin into anterodorsal and posterodorsal parts.