Ultrastructure of gland cells associated with the chaetal follicles in the clitellar region of Lumbricus friendi Cognetti, 1904 (Oligochaeta).

The ultrastructure of the gland cells associated with the chaetal follicles of the ventral clitellar epithelium is described in the earthworm Lumbricus friendi. Regarding their secretory granules, two cell types (GS1 and GS2) have been identified. Secretory granules of both cell types show a large, electron-dense core which is homogeneous in the GS1 type and irregularly shaped in the GS2 type. Crystalline inclusions embedded in the GS1 granule matrix is characteristic of the GS1 cell type. Both types of secretory granules are directly extruded by exocytosis into the chaetal follicle lumen. The basal regions show the typical cytological features of cells which are capable of synthesis of both protein and complex carbohydrates. The results and the functional significance of the two cell types studied are discussed and compared with that is known in other lumbricids.