The presence and location of small cardioactive-like peptides in larvae of Crassostrea virginica

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.