Schistosoma mansoni: a new parenchymal cell in cercariae.

A new type of cell has been identified in cercariae of Schistosoma mansoni. The perikarya (cell bodies) of these cells were located in the body (midsegment), in an area oral to the acetabulum (ventral sucker). Cytoplasmic processes extending from the perikarya ramified throughout the parenchyma of the anterior organ (oral sucker), body, and tail segments by following the path of the nerve processes from the neuropile. The perikarya of these cells had heterochromatic nuclei and a predominance of particulate material and granules (240-360 nm) in their cytoplasm. Aggregates of granules (240-360 nm) and associated vesicles (34 nm) were scattered throughout the cytoplasmic processes of the cells and formed distinct varicosed areas. These processes often connected to the tegument in the midsegment (body) of the cercariae. The granules and associated vesicles reacted (became electron dense) with fixatives reported to be detectors of biogenic amines: The glutaraldehyde/osmium tetroxide fixation procedure rendered the granules electron dense while the glutaraldehyde/chromate/osmium tetroxide fixation procedure rendered the granules and the associated vesicles electron dense. The chromate solution of the latter procedure was responsible for the electron density of the associated vesicles. The morphology of these cells (their long ramifying cytoplasmic processes) and their reaction to chromium suggests that they are probably biogenic aminergic sensory cells.