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The first description of vitellogenesis in the Diphyllidea is presented in this paper. Though the type of vitellogenesis and mature vitellocyte in Echinobothrium euterpes appear to be unique among the Eucestoda, however, they somewhat resemble that observed in the two orders of the lower cestodes, Tetraphyllidea and Proteocephalidea. Vitellocyte maturation is characterized by: (1) an increase in cell volume; (2) extensive development of short, parallel, frequently concentric cisternae of GER that produce dense proteinaceous granules; (3) development of Golgi complexes engaged in packaging this material; (4) progressive formation of saturated lipid droplets; their continuous enlargement and fusion; (5) formation of small accumulations of glycogen particles scattered between and among lipid droplets in the cytoplasm of maturing vitellocytes; (6) concentration of dense proteinaceous granules in the peripheral layer of cytoplasm, around the cell plasma membrane; and (7) vacuolization of cytoplasm of mature vitellocytes accompanied by a rapid increase in its volume. A new, unreported type of dense proteinaceous granules, situated around the limiting plasma membranes of mature vitellocytes, is described. Vitellogenesis evidently differs from that with typical shell-globules and shell-globule clusters previously reported in other taxa of lower cestodes. Cytochemical staining with periodic acidthiosemicarbazide-silver proteinate for glycogen indicates a strongly positive reaction for glycogen particles between and around large unsaturated lipid droplets of the maturing and mature vitellocytes. Some hypotheses concerning the interrelationship between this pattern of vitellogenesis, possible mode of egg formation, embryonic development and diphyllidean life cycle, and their phylogenetic implications are drawn and discussed.
In total, 404 fishes of 34 species caught in the Weddell Sea were examined, including four specimens of skates, Bathyraja maccaini and Bathyraja sp., and 23 specimens of the gadiform fish, Macrounis whitsoni (the only three species infected with adult Cestoda). Skates were infected with four representatives of the order Tetraphyllidea, Marsupiobothrium awii sp. n., Anthocephalum siedlecka (syn. Phyllobothrium siedleckii), Anthocephalum arctowskii (syn. Phyllobothrium arctowskii), Oncobothrium antarcticum. The three last species were first described in the South Shetland Islands area. Phyllobothrium siedleckii from B. maccaini (new host) and P. arctowskii from Bathyraja sp. are transferred to the genus Anthocephalum and their descriptions are emended. Marsupiobothrium awii sp. n. from B. maccaini is characterised by: apolytic strobila; scolex with four sessile, jar-like bothridia, each with opening provided with a ring of muscles and submarginal sucker; 120-150 testes; vagina with dilatation in proximal part and sphincter present distally; eggs 0.016 x 0.017 mm. Differential diagnosis with remaining species of the Marsupiobothrium is given. Oncobothrium antarcticum was found in B. maccaini (new host). M. whitsoni was infected with one pseudophyllidean species, Parabothriocephalus johnstoni, previously known as only from the same host in the Indian sector of the Antarctic Ocean.
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