Ultrastructure and functional significance of intestinojunctional spermathecae in enchytraeids (Oligochaeta, Annelida)

Abstract

The ultrastructure of paired seminal receptacles (spermathecae) communicating directly with the intestinal tract of three enchytraeid species ( Enchytraeus crypticus, Fridericia montafonensis and Marionina preclitellochaeta) is described and compared with blind receptacles of an Achaeta species. Although the same in general configuration, comprising 1. an ectal part consisting of a single-layered epithelium with an inner lining of cuticle, 2. gland cells (rosette glands) around the outer orifice, 3. an external muscular coat, and 4. an ental part that may form a greatly expanded ampulla, the spermathecae of these three species exhibit certain marked differences in the individual parts. In F. montafonensis, the two ampullae are subdivided to form diverticula, where intact sperm are stored, and a common chamber that contains more or less degenerate sperm and opens into the oesophagus dorsally. In M. preclitellochaeta, sections revealed phagocytosis of sperm in the wall cells of the ampullae, as well as direct transfer of sperm bundles into the intestinal tract. There is evidence that the ampullae of this species are intestinal pockets and not part of the epidermal invaginations. The spermathecae of E. crypticus do not expand to form ampullae. Function of the spermathecae is discussed, as is the trophic significance of the allosperm, particularly in relation to the hermaphroditic organization and small body size of these animals.