Abstract. 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.
We examined the presence and location of small cardioactive peptide (SCP)‐like neuropeptides in both the central and peripheral nervous systems of D‐hinge, newly eyed, and pediveliger larvae of Crassostrea virginica. Results indicate that SCP‐like substances are present early in development (D‐hinge larvae), and that presence in the central and peripheral nervous systems increases as the larva develops toward metamorphic competence (pediveliger larvae). In addition, in newly eyed and pediveliger larvae, SCP‐like labeling is found in a varying number of neurons within all central ganglia, with the possible exception of the accessory ganglia. Varicose labeling of axons is also documented within the ganglia, commissures, and connectives, as well as in peripheral nerves. Peripheral tissues innervated by axons exhibiting SCP‐like immunoreactivity include the velum, foot, esophagus, mantle, and various musculatures. As indicated by the location of SCP‐like labeling in various organs and tissues, it is likely that these neuropeptides modulate muscle contraction or ciliary beating in molluscan larvae such as those of C. virginica.
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