Mollusca: Bivalvia

Bivalvia (Lamellibranchiata, Pelecypoda) is a large class of laterally compressed animals characterized by two calcified variably flattened to deeply cupped valves that are attached to each other at the dorsal surface with teeth spanned by a flexible hinge ligament. Bivalve larvae are amazingly similar from fertilization until metamorphosis which makes learning larval anatomy easy, but identification of larvae from different species difficult when samples are collected from the wild environment. Based on their overall morphology, bivalves are separated into five subclasses but are practically placed into the following groups: clams, cockles, mussels, scallops, and oysters. This chapter discusses the anatomy of the clam and then describes important anatomic differences in oysters, scallops, mussels, and cockles. The tubules in scallops have been described as more acinar-like. The absorptive cells in histologic sections often appear enlarged, are highly vacuolated and have been described as adipocyte-like