FOREST, S.; LINDSAY, S. M.; University of Maine, Orono: Comparative Morphology of the Nervous System and Peripheral Sensory Cells in Three Species of Spionid Polychaetes

The organization of the nervous system, innervation of peripheral sensory cells and the distribution of serotonin (5-HT) and FMRF-amide containing neurons were compared in three species of Spionid polychaetes: Dipolydora quadrilobata, Pygospio elegans and Streblospio benedicti. Spionid polychaetes are tube-building marine worms with a cosmopolitain distrubution from estuarine to deep-sea environments that are capable of deposit and suspension feeding with a pair of ciliated, tentaculate anterior feeding appendages (palps). Using immunohistochemistry in conjunction with confocal laser scanning microscopy, CNS and peripheral nerves were labeled and then visualized with digital imaging software. Antibodies directed against acetylated α-tubulin, targeting nerve axon and cilia axoneme microtubules, show the innervation of ciliated cells in the palps of each species. This provides evidence of their sensory nature, the precise modality of which remains unknown although a chemosensory role is hypothesized. 5-HT immunoreactivity revealed: (1) previously undescribed structures underlying the food groove of the palps; (2) palp nerves and their connections with the cerebral ganglion and (3) segmental patterns of nerves and perikaria in the ventral nerve cord. FMRF-amide immunoreactivity allowed the visualization of: (1) the general nervous system; (2) palp nerves and the cerebral ganglion and (3) metamerically repeated patterns of perikaria in the ventral nerve cord and periphery. Activity-dependent labeling of sensory cells and the possible role of 5-HT in feeding behavior is currently being investigated.