Unusual granules in the ejaculatory duct of a Microphthalmus species (Polychaeta, Annelida)

The paired prominent ejaculatory ducts of the hermaphroditic polychaete Microphthalmus cf. listensis are surrounded by gland cells the processes of which penetrate the ducts themselves. These cells produce, in separate regions, two different types of spherical granules. Type I is composed of an electron dense and an electron lucent part. Type II granules contain a tubular filament that forms a single or double spiral in the periphery of a more or less unstructured electron dense material. Golgi vesicles give rise to this granule type. During the passage of sperm, these granules are obviously discharged into the lumen of the duct. Here they change form and probably dissolve. Their function is as yet unknown; capacitation of sperm is assumed.