CROLL, RP; HOCHBERG*, R*; Dalhousie University, Nova Scotia; Smithsonian Marine Station, FL: Neomeniomorpha-Solenogastres (Aplacophora): Insights into the Neuromuscular System of Primitive Mollusca

Neomeniomorpha (Solenogastres) is a small and monophyletic taxon of marine, shell-less molluscs that share a potentially primitive phylogenetic position with species of Chaetodermomorpha (Caudofoveata). Species of both clades are poorly cephalized, wormlike, and possess a suite of plesiomorphic morphologies that characterize them as primitive molluscs. In this study, three species of interstitial solenogastres (Tegulaherpia(2), Meiomenia (1)) were studied using a combination of confocal microscopy, phalloidin labeling, and immunohistochemistry to gain insight into the structure of the neuromuscular system. Antibodies to serotonin, FMRFamide, and SCPb allowed for visualization of the nervous system including cerebral and pedal ganglia, pedal and visceral nerve cords, intercordal commissures, and innervation of the bodywall, velum, and pedal pit. 5HT-immunoreactivity provided the most revealing details, allowing for unambiguous demonstration of neuronal perikarya and processes throughout the body. Phalloidin was used to visualize the bodywall and gut musculature, exposing a 3-D gridwork of circular, diagonal, longitudinal, and dorsoventral muscles. Results reveal that solenogastres possess a neuromuscular system analogous to the �new molluscan archetype (HAM)� presented by Haszprunar, and application of the aforementioned methodologies (cLSM, immunohistochemistry) will provide valuable insights into the structure and evolution of aplacophoran molluscs.