Ultrastructure of the anterior salivary gland cells of the giant leech, Haementeria ghilianii (Annelida, Hirudinea).

The giant anterior salivary gland cells from the large mammalian blood-sucking, glossiphoniid leech, Haementeria ghilianii, can be subdivided into three morphologically and functionally distinct regions: 1) a soma, responsible for the synthesis and storage of secretory products; 2) a long cell process, responsible for the storage and intracellular transport of the secretory vesicles; and 3) the site of exocytosis at the process terminal. The giant somata are densely packed with secretory vesicles. Deep plasmalemmal invaginations invade the soma and form an extensive system of extracellular lacunae. The rough endoplasmic reticulum (ER) and the Golgi apparatus are organized in the cell periphery, near the highly branched nucleus, and along the lacunae. The somata taper into long processes extending over several centimeters to the proboscis tip. These contain secretory vesicles through their whole length. In the process periphery, the vesicles are completely ensheathed by a concentric subplasmalemmal smooth ER cisterna. This originates deeply within the soma and extends through the whole cell process to its terminal. The ER provides support for up to several hundred longitudinally oriented microtubules. Secretion occurs at the very tip of the cell processes, each of which terminates at the proboscis tip at the base of a cuticular pore. We found synapses close to the sites of exocytosis, providing morphological evidence for neuronal control of secretion.