Ultrastructure of the cirrus sac of the male strobila of Shipleya inermis (Fuhrmann, 1908) (Cestoda: Cyclophyllidea)

Abstract This study was designed to provide information on the ultrastructural traits of the cirrus sac of the male strobila of the dioecious cyclophyllidean tapeworm, Shipleya inermis Fuhrmann, 1908 from the small intestine of long-billed dowitchers, Limnodromus scolopaceus, in Chukotka, Russia. The cirrus sac is characterised by a thick muscular wall (comprising about 20 layers of longitudinal muscles) with the muscle cells being located outside the wall along the peripheral muscle layer and the presence of a thick, fibrillar septum inside the sac along the inner muscle layer of the wall. The epithelium of the intrabursal ducts is syncytial and has sunken perikarya. The ejaculatory duct is characterised by surface luminal microvilli and a large number of the sunken perikarya producing electron-dense secretory granules, which discharge into the duct lumen as an apocrine secretion. The cirrus is armed with two types of sclerotized structures formed by its epithelium, hooks of about 25 μm in length and microthrix-like structures on its luminal surface. The hooks are sigmoid in shape, have a blade circular in transverse section and about 3.5 μm in width, and taper at both extremities. The hook body consists of moderately electron-dense material mixed with a more electron-dense material and an electron-lucent core. The hook roots lie within the cirrus epithelium, where their lateral margins are composed of a thin covering of electrondense material with narrow lateral extensions. The usefulness of the ultrastructural characters of the cirrus sac as indicators of phylogenetic relationships within the Eucestoda is discussed.