Histofluorescent and Ultrastructural Identification of Aminergic Processes in the Opisthaptor of the Marine Monogene, Microcotyle sebastis (Polyopisthocotylea: Microcotylinae)

The opisthaptoral clamp region of Microcotyle sebastis Goto, 1894, was examined for aminergic processes by histofluorescent and ultrastructural techniques. Glyoxylic acid-induced fluorescence, indicative of catecholamines, revealed blue/green varicosities and longitudinal processes directly associated with clamp elements. Ultrastructural examination of nerve processes in close histologic proximity to those found by fluorescence microscopy revealed numerous small dense and/or dense-core vesicles within the clamp musculature, as well as processes containing both electron-dense and lucent vesicles in the opisthaptoral neuropil. Two nerve bundles, surrounded by clamp basal lamina and epidermis within the clamp cavity, were found situated on either side of the median clamp sclerite. A nerve bundle was also found on the interior surface of the clamp cavity, approximately % the distance between the median clamp sclerite and the lateral sclerite elements. This bundle was serially sectioned and a single uniciliated receptor was found. Although it is speculated that these receptors exhibit bilateral symmetry, only 1 receptor was found. Other processes within the clamp musculature and in the opisthaptoral neuropil contained vesicle types consistent with cholinergic, aminergic, and peptidergic morphology. Nerve location and associated vesicle morphology within the clamp suggest a sensory/neuromodulatory role associated with sensory receptors. A role other than sensory is suggested for nerves containing small dense/ dense-core vesicles and/or a combination of other vesicle types within nerves adjacent to or within the haptoral neuropil.