Ultrastructure of the ovary, ovicapt and oviduct of the spathebothriidean tapeworm Didymobothrium rudolphii [Monticelli, 1890]

The ultrastructural details are presented of the ovary, ovicapt and oviduct of the spathebothriidean tapeworm Didymobothrium rudolphii (Monticelli, 1890) from the intestine of the sand sole Solea lascaris. Oogonia, maturing oocytes and mature oocytes are surrounded by a syncytial interstitial cytoplasm, one of the distinctive traits of which is the presence of numerous myelin-like bodies. Oocyte inclusions comprise cortical granules and a small number of lipid droplets. The thickened, nucleated epithelium of the ovicapt lacks any apical structure and is a prolongation of the narrow ovarian epithelium. The muscular sphincter of the ovicapt is formed by a band of longitudinal muscles and bands of radial muscles at right angles to the longitudinal layer, and numerous myocytes surround the ovicapt wall. The oviduct of D. rudolphii is subdivided into three regions: (1) the proximal oviduct; (2) the fertilization chamber — the region distal to the point of entry of the duct from the seminal receptacle; and (3) the ovovitelline duct — the region distal to the point of entry of the duct from the vitelline reservoir. A comparative analysis is made between the structures of the ovary, ovicapt and oviduct of D. rudolphii and those of two other spathebothriideans, Cyathocephalus truncatus and Diplocotyle olrikii, with a discussion of ultrastructural traits that might be used as taxonomic criteria within the order Spathebothriidea.