NEDVED, B. T.*; HADFIELD, M. G.; Uni. of Hawaii, Kewalo Marine Laboratory; Uni. of Hawaii, Kewalo Marine Laboratory: Remodeling of larval nervous system during metamorphosis of Hydroides elegans

Metamorphosis of many marine invertebrate larvae occurs rapidly and is triggered by the binding of specific external cues with appropriate larval receptors. This binding activates a cascade of events that culminate with the loss or reorganization of larval tissues and the appearance of adult structures. Metamorphosis of the serpulid polychaete Hydroides elegans is probably triggered by the binding of bacterial exopolymers to sensory cells located in the apical sensory organ (ASO). This process is characterized by: the secretion of a proteinaceous primary tube; restriction of the collar region; loss of trochal cilia; elongation of pygidial region; and development of the branchial crown. While the time course and the external morphogenic events of this process have been determined, relatively little is known about the fate of the central nervous system during metamorphosis. At the time of metamorphic competence, the central nervous system is composed of both larval and juvenile elements. While the juvenile elements (the cerebral ganglion, circumesophageal connectives, and ventral nerve cords) persist and continue to develop post-metamorphosis, the fate of the larval nervous system (the ASO, trochal nerves, and suboral complex) remains unclear. Antibodies raised against serotonin, FRMF-amide, and tyrosine hydroxylase are immunoreactive to subsets of cells within both the larval and juvenile nervous systems and provide a means for tracking these cells through the metamorphic progression. In this immunocytochemical study, these antibodies and scanning confocal microscopy were used to determine the fate of larval nervous system during metamorphosis and early juvenile development