Ultrastructure and Cytochemistry of the Mature Spermatozoon of Khawia Armeniaca (Cholodkovsky, 1915) (Caryophyllidea: Lytocestidae), a Parasite of Capoeta Capoeta Sevangi (De Filippi, 1865) (Teleostei, Cyprinidae).

The mature spermatozoon of Khawia armeniaca, a monozoic caryophyllidean parasite of templar fish Capoeta capoeta sevangi (De Filippi, 1865) from the Lake Sevan, Armenia, has been studied using transmission electron microscopy and cytochemical technique of Thiéry (1967) for the first time. The mature spermatozoon of K. armeniaca consists of a single axoneme with the 9+'1' trepaxonematan structure, cortical microtubules and nucleus which are situated parallel to the longitudinal axis of the spermatozoon, and a moderately electrondense cytoplasm with glycogen particles. The cortical microtubules are arranged in one continuous semicircle beneath the plasma membrane in Region II and anterior part of Region III of the mature spermatozoon. The two opposite rows of cortical microtubules are observed in the remaining nuclear and at the beginning of the postnuclear part (Regions III, IV) of the male gamete The number of cortical microtubules is remarkably variable in the spermatozoa of various Khawia species. K. armeniaca exhibits the highest number of cortical microtubules in comparison with K. sinensis and K. rossittensis. Glycogen was detected in the cytoplasm of prenuclear (II), nuclear (III) and postnuclear (IV) regions with different ultrastructural organization of the mature spermatozoon of K. armeniaca. Variations of sperm ultrastructural characters within caryophyllideans and other cestodes are discussed.

Histopathological and ultrastructural studies of the tapeworm Monobothrium wageneri (Caryophyllidea) in the intestinal tract of tench Tinca tinca.

Monobothrium wageneri is a monozoic caryophyllidean tapeworm of tench Tinca tinca. The pathological changes caused by this parasite within the intestinal tract of wild tench are described for the first time. Parasites were found attached to the anterior third of the intestine in tight clusters comprising up to 109 tapeworms. Infection was associated with the formation of raised inflammatory swellings surrounding the parasites. This host response, combined with the deep penetration of the scolex into the gut wall, formed a very firm seat of parasite attachment. Histopathological changes were characterised by a pronounced fibrogranulomatous lesion that extended through all layers of the intestine. This was accompanied by haemorrhage, oedema, necrosis and degeneration of the muscularis. A marked eosinophilic interface layer between the scolex of the tapeworm and gut wall indicated intimate host-parasite contact. Ultrastructural examinations revealed coniform spinitriches covering the neck and lateral sides of the scolex and capilliform filitriches present on the apical end of the scolex. Numerous glandular cytons (tegumental glands) were recorded throughout the scolex tegument. Large numbers of secretory granules discharged from the glands through a network of processes onto the scolex surface were consistent with distancing the cellular responses of the host. Observations of severe inflammatory lesions, partial intestinal occlusion and the potential for intestinal perforation represent important pathological changes that are consistent with loss of normal gut function. The lesions associated with the attachment of M. wageneri are more severe than those recorded for any other tapeworm of British freshwater fish.

Ultrastructure of the neodermal sclerites of Gyrocotyle urna Grube and Wagener, 1852 (Gyrocotylidea, Cestoda).

Body sclerites of Gyrocotyle urna Grube and Wagener, 1852, parasites of Chimaera monstrosa L., were studied by transmission electron microscopy. Each sclerite consists of ten to 15 concentric layers varying in electron density and thickness. The sclerites insert in pockets whose epithelia are continuous with the body neodermis but are 14 times thinner. The pocket neodermis bears surface projections with an inner electron-dense cylinder and a small electron-dense cap at their tip. It is surrounded by a well-elaborated basement lamina and bundles of musculature; the perikarya of this part of the neodermis lie underneath the basement membrane. The luminal plasma membrane of the pockets is covered by a coat originating from vesicles and dense bodies most probably discharged from the pocket neodermis, supporting the assumption that the deposition of this material builds up the sclerites. Therefore, sclerites are derivatives of the neodermis. With regard to their ultrastructure, sclerites resemble the calcareous corpuscles of other cestode taxa. They represent a useful phylogenetic character and are an autapomorphy of the Gyrocotylidea.

On the position of Archigetes and its bearing on the early evolution of the tapeworms.

The tapeworm Archigetes sieboldi Leuckart, 1878 (Platyhelminthes: Cestoda: Caryophyllidea) has been cited as a likely representative of the "protocestode" condition, owing to its lack of segmentation and ability to attain sexual maturity in the invertebrate host (aquatic oligochaetes). The idea has been variously amplified or rejected in the literature, although the actual phylogenetic position of the species has not been investigated until now. New collections of Archigetes sp. from both its vertebrate and invertebrate hosts provided the opportunity to estimate its phylogenetic position with the use of molecular systematics, while prompting new analyses aimed at assessing the early diversification of the Cestoda. Additional collections representing the Amphilinidea, Caryophyllidea, and Gyrocotylidea were combined with published gene sequences to construct data sets of complete 18S (110 taxa) and partial (D1-D3) 28S (107 taxa) rDNA sequences, including 8 neodermatan outgroup taxa. Estimates resulting from Bayesian inference, maximum likelihood, and maximum parsimony analyses of the separate and combined data sets supported a derived position of the genus within the Caryophyllidea, and thus reject the idea that Archigetes sp. may exemplify a "primitive" condition. Topological constraint analyses rejected the hypothesis that Archigetes represents the most basal lineage of the Eucestoda, but did not rule out that it could represent the earliest branching taxon of the Caryophyllidea. In all analyses, the Eucestoda were monophyletic and supported basal positions of the nonsegmented Caryophyllidea and Spathebothriidea relative to other major lineages of the Eucestoda, implying that segmentation is a derived feature of the common ancestor of the di- and tetrafossate eucestodes. However, constraint analyses could not provide unequivocal evidence as to the precise branching patterns of the cestodarian, spathebothriidean, and caryophyllidean lineages. Phylogenetic analyses favor the interpretation that sexual maturity of Archigetes sp. in the invertebrate host, and similar examples in members of the Spathebothriidea, are the result of progenesis and have little if any bearing on understanding the protocestode condition.