Umbo function clam Place a clam in a dissecting tray and identify the anterior and posterior ends of the clam as well as the dorsal, ventral, & lateral surfaces. Figure 1 dorsal (top surface) ventral (bottom surface) anterior posterior umbo left Place a clam in a dissecting tray and identify the anterior and posterior ends of the clam as well as the dorsal, ventral, & lateral surfaces. Growth ring Northern hard clam, Mercenaria mercenaria External Clam Shell Anatomy 1. Many times the umbo appears worn with the dark outer layers of the shell removed, exposing the iridescent nacre/mother of pearl. The umbo is circular in shape and is the oldest section of the shell. 5. 0 (1 review) Flashcards; Learn; Test; protects the clam from predators and also allows the clam to open and close. The umbo (plural umbones or umbos) is the vaguely defined, often most prominent, highest part of each valve of the shell of a bivalve or univalve mollusc. 4. Dorsal or upper 5. mcucrjjsxfdfkfqmqmtmenoaqbqxlebxwesbpjduwjmljhijcwxzfwtfulmyivqyfgavofblk