Reproduction of trematodes in the molluscan host: an ultrastructural study of the germinal mass and brood cavity in daughter rediae of Tristriata anatis Belopolskaia, 1953 (Digenea: Notocotylidae)
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This study describes the fine structure of the germinal mass in daughter rediae of Tristriata anatis. The germinal mass consists of undifferentiated cells, germinal cells and supporting cells and contains numerous cercarial embryos up to tail bud stage. Supporting cells and their outgrowths form a tight meshwork of the germinal mass. In its basal part, this meshwork serves as scaffolding for undifferentiated and germinal cells, naked cell aggregates and early germinal balls. More mature embryos are located apically. The hypertrophied supporting tissue appears to be involved in an intensive transport of substances, as indicated by abundant gap junctions between cell outgrowths and numerous pinocytotic vesicles and microtubules in their cytoplasm. Germinal cells contain annulate lamellae and the nuage, typical organelles of animal oocytes. In young rediae containing embryonic cercariae at the tail bud stage, the supporting tissue starts to degenerate in the apical part of the germinal mass, and a primordial brood cavity emerges though it develops fully only in mature rediae containing late embryonic cercariae. An unusual feature of the germinal mass in T. anatis rediae is an enhancement of the embryo brooding function. At the same time, the performance of this function by the brood cavity is reduced. This is the first time such a redistribution of the embryo brooding function between the germinal mass and the brood cavity has been reported.
KeywordsTristriata anatis Reproduction of redia Ultrastructure Germinal mass Germinal cell Brood cavity
We are grateful to Natalia Lentsman for her help with the translation of the MS into English. We would like to thank the reviewers for their valuable comments and suggestions. Scientific research was performed using equipment of the “Taxon” Research Resource Center (http://www.ckp-rf.ru/ckp/3038/) of the Zoological Institute of the Russian Academy of Sciences (St. Petersburg).
This work was supported by the Russian Foundation for Basic Research (Grant No 16-04-00753) and by the programme of the Russian Academy of Sciences of the Zoological Institute No. АААА-А17-117030310322-3.
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