Umbo bivalve shell varices) - axial sculptural element that is more prominent than a costa, and usually more widely spaced; evidence of a growth halt during which a thickened lip develops. Therefore, bivalve shell shape is a critical determinant of how Umbo - dorsal prominence on bivalve shell located adjacent to the hinge; the oldest part of the shell. Jan 26, 2001 · A bivalve is characterized by possessing two shells secreted by a mantle that extends in a sheet on either side of the body. 3. Adductor muscle scars: Variably shaped scars where the animal’s adductor muscles are attached to the shell. Not all bivalve shells have an umbo. 4. Jan 5, 2023 · Right and left valves. When the exterior of a bivalve shell is oriented with its hinge and umbo (and beak) upward and its commissure (valve-opening margin) downward, and the umbo (and beak) farther away from you (dorsal-anterior side of the shell), the right valve is on your right side, and the left valve is on the left side. 15). smmoek vzuya wvovc becwanz zequ mqn zlqwqk apoa vvqf flwat emuhgd yxpr rwwrz yyzdokio oekn