Characterization of the central nervous system and various peripheral innervations during larval development of the oyster Crassostrea virginica

. Although a few investigations have considered neuronal aspects of bivalve larval ontogeny, the central and peripheral nervous systems of bivalve veligers have yet to be described in detail. This study provides a detailed description of central and peripheral components of the larval nervous system in the Eastern oyster, Crassostrea virginica. Larvae at the D-hinge, newly eyed and pediveliger stages were examined at the light level by means of serial histological section sets. D-hinge larvae were found to have limited neurogenesis with only an anterior gangliar rudiment being present. As development progressed to the newly eyed larval stage, a single apical ganglion and paired cerebro-pleural, pedal, and visceral ganglia were identified, forming a typical bivalve central nervous system loop. The nervous system of pediveligers was similar to that of newly eyed larvae, but added an additional accessory ganglion on the left and right sides, posterior to each gill rudiment. A posterior visceral commissure was also present. Various peripheral innervations were also documented, including nerves extending from the pedal and visceral ganglia in both newly eyed and pediveliger larvae. Furthermore, several neuronal processes, such as the mantle, ventral osphradial, anterior adductor and dorsal esophageal nerves were seen connecting to ganglia. This investigation provides an essential histological characterization of the complex nervous system present in bivalve oyster larvae.