A simple neuronal system characterized by a monoclonal antibody to SCP neuropeptides in embryos and larvae of Tritonia diomedea (Gastropoda, Nudibranchia).

SCP-like antigenicity is first present in Tritonia diomedea in small cells of the cerebral ganglia and a single axon crossing the cerebral commissure of 8-day-old embryos. Other axons and neurons become antigenic as the larva develops. At 4-9 days after larvae hatch from the egg mass, 2 additional pairs of neurons are labeled. Axons extend from one pair to the left cerebral ganglion and from the other to the right. A second labeled axon is present across the cerebral commissure. In metamorphically competent larvae the cerebral and pedal neuropils, as well as two neurons in the buccal ganglia with axon(s?) across the commissure, are antigenic. The change in antigenicity as the larva becomes competent is presumably preparatory for juvenile life. The labeled buccal neurons may be B12, which are known to contain SCPs, extend an axon across the buccal commissure, and function in adult feeding behavior. The two large neurons strongly labeled by rabbit polyclonal antibodies against FMRFamide are clearly different from neurons labeled by monoclonal antibody against SCPs. This result supports the contention that different antigens are labeled by these two immune probes.