241 Fine structure of the male reproductive ducts, vagina and seminal receptacle of Cyathocephalus truncatus (Cestoda: Spathebothriidea) Larisa G. Poddubnaya 1 , John S. Mackiewicz 2 , Magdaléna Bruňanská 3,4 and Bahram S. Dezfuli 5 1 Institute of Biology of Inland Waters, Russian Academy of Sciences, 152742 Borok, Yaroslavl Province, Russia; 2 Department of Biological Sciences, State University of New York, Albany, NY 12222, USA; 3 Institute of Parasitology, Academy of Sciences of the Czech Republic, Branišovská 31, 370 05 České Budějovice, Czech Republic; 4 Parasitological Institute, Slovak Academy of Sciences, Hlinkova 3, 040 01 Košice, Slovakia; 5 Department of Biology, University of Ferrara, St. Borsari, 46, 44100 Ferrara, Italy Key words: Cyathocephalus truncatus, ultrastructure, male ducts, accessory glands, vagina, seminal receptacle Abstract. Fine structure of the vas efferens, vas deferens, ejaculatory duct with accessory glands and vagina with seminal recep- tacle is described in the spathebothriidean tapeworm, Cyathocephalus truncatus (Pallas, 1781) Kessler, 1868. The numerous well-developed prostate glands are characterised by having secretory granules with an electron-dense core surrounded by a ma- trix of lower electron density. Coalescence of the outer part of the granules with each other takes place in the terminal end of the secretory ducts. The position of prostate glands around the proximal part of the cirrus pouch and terminating in the ejaculatory duct is a characteristic feature of the Spathebothriidea. Up to 20 closely arranged muscle layers make up the muscular cirrus pouch wall with 4 well-developed muscular layers in the ejaculatory duct and cirrus. Both the cirrus and the vagina are covered with the same uniform cone-shaped microtriches. The vagina has an extensive seminal receptacle. All of these structures are well-adapted to insure successful sperm transfer involving ejaculation and storage, probably for both self- and cross-insemina- tion. Cyathocephalus truncatus has a cirrus similar to that of the monozoic, progenetic caryophyllidean, Archigetes sieboldi and well-developed prostate glands like those of the polyzoic pseudophyllidean, Diphyllobothrium latum. The ultrastructural aspects of the male and female reproductive system of C. truncatus are compared with those of other tapeworms. The Spathebothriidea is a small group of polyzoic tapeworms with a polypleuroid body type, that is, with proglottization but no defined segments (Mackiewicz 2003). This lack of segmentation has been explained as either secondarily derived from a strobilate tapeworm (Fuhrmann 1931, Joyeux and Baer 1961, Protasova and Roytman 1995), or ancestral to the monozoic caryophyl- lideans (Nybelin 1922, Olson and Caira 1999). How- ever, the non-segmented but polyzoic spathebothri- ideans and monozoic caryophyllideans have been deter- mined to represent the ancestral condition and occupy a basal position on the cestode evolutionary tree (Mariaux 1998, Hoberg et al. 2001, Mariaux and Olson 2001, Olson et al. 2001). It is clear that the systematic position and relationship of the Spathebothriidea to other ces- todes is far from resolved. There is no modern, detailed treatment of the Spathe- bothriidea (Gibson 1994). Most of the information on the group deals with aspects of general biology, mor- phology or taxonomy (Nybelin 1922, Wardle and McLeod 1952, Gibson 1994, Protasova and Roytman 1995, Kearn 1998, Okaka 2000). Little information is available on the anatomy and morphology at the ultra- structural level for any species. Ultrastructural observa- tions on genital organs of members of the Spathe- bothriidea is limited to the study of uterine and prostate glands in progenetic Diplocotyle olrikii (Davydov et al. 1997) and the structure of spermatozoa in Bothrimonus sturionis (MacKinnon and Burt 1984). The present con- tribution describes the fine structure of the male ducts with accessory glands and vagina with seminal recepta- cle of the female system in Cyathocephalus truncatus (Pallas, 1781) Kessler, 1868. Detailed morphological data of the reproductive system may help in the analysis of interrelationships of the Spathebothriidea among the lower tapeworms. MATERIALS AND METHODS Adult Cyathocephalus truncatus were recovered from the pyloric appendices of two salmonid fish species, grayling (Thymallus arcticus baicalensis Dybowski) from Lake Baikal (Russia), and brown trout (Salmo trutta) from Carmigniano of Brenta (province of Padua, North Italy). The worms from Lake Baikal were cut into small pieces and fixed in 3% glu- taraldehyde in 0.1 M phosphate buffer (pH 7.4) for 6 h at 4°C. They were postfixed in 1% osmium tetroxide in 0.1 M phos- phate buffer for 1 h at 4°C. The worms from Italy were fixed in 2% glutaraldehyde in 0.1 M sodium cacodylate buffer (pH 7.2) for 3.5 h at 4°C. Postfixation followed in 1% osmium tetroxide in 0.1 M cacodylate buffer for 2 h at 4°C. The mate- FOLIA PARASITOLOGICA 52: 241–250, 2005 Address for correspondence: L.G. Poddubnaya, Institute of Biology of Inland Waters, Russian Academy of Sciences, 152742 Borok, Yaroslavl Province, Russia. Phone/Fax: ++7 8547 240 42; poddubny@ibiw.yaroslavl.ru