Meeting Abstract

P3.82  Jan. 6  Serotonin-immunoreactivity in the head-foot complex of an interstitial acochlidean reveals the conservative distribution of 5-HT in the opisthobranch nervous system HOCHBERG, Rick; Univ. of Massachusetts, Lowell rick_hochberg@uml.edu

Species of Acochlidea (Mollusca) are common members of the marine interstitial environment and defined in part by their minuscule size and highly divergent morphology relative to other benthic opisthobranchs. Despite these differences, acochlideans such as species of Asperspina display many plesiomorphic characteristics including an unfused condition of their neural ganglia. To gain insight into the distribution of specific neural subsets within the acochlidean nervous system, a species of Asperspina was studied using anti-serotonin immunohistochemistry and epifluorescence and confocal laser scanning microscopy. Results reveal at least four significant similarities between Asperspina and the larger opisthobranchs (e.g., Aplysia, Pleurobranchaea, Tritonia): 1) Immunoreactive perikarya form regional clusters within the cerebral and pedal ganglia; 2) Immunoreactive perikarya are absent from the pleural ganglia; 3) Serotonergic innervation of the rhinophores originates from the cerebral ganglion and not the rhinophoral ganglion; and 4) Peripheral innervation of the the epithelium, muscles, and locomotory cilia arises almost exclusively from the pedal and accessory ganglia. In conclusion, the distribiution of serotonergic elements in the acochlidean nervous system appears, perhaps surprisingly, similar to species that are orders of magnitude larger. These similarities highlight the conservative nature of the opisthobranch nervous system despite drastic evolutionary modifications in animal size and lfiestyle