MORPHOLOGY OF LEECH SENSILLA: OBSERVATIONS WITH THE SCANNING ELECTRON MICROSCOPE

¹ Department of Biology, University of Virginia, Charlottesville, Va 22901

The external morphology of the body wall of the medicinal leech, Hirudo medicinalis, was investigated with the scanning electron microscope. At high magnification, most of the leech body wall has a granular appearance punctuated by numerous small pores. The disc-shaped sensory sensilla are easily distinguished from the surrounding body wall by the absence of pores and the presence of numerous filiform projections in the central region of each sensillum. Two types of projections can be distinguished: single, 3-9 µm long "S-hairs" and grouped (i.e., composed of several subunits), 1-2 µm long "G-hairs." Each sensillum supports 40-90 S-hairs and 15-20 G-hairs. The S-hairs may be the sensory structures mediating leech sensitivity to low amplitude water movements.

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