Trematode reproduction in the molluscan host: an ultrastructural study of the germinal mass in the rediae of Himasthla elongata (Mehlis, 1831) (Digenea: Echinostomatidae)
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The germinal mass in Himasthla elongata rediae was studied in detail using transmission electron microscopy. It was shown to be a specialized reproductive organ consisting of germinal cells at various maturation stages, supporting cells and stem cells. The germinal mass also contains early cercarial embryos emerging as a result of cleavage division of mature germinal cells. The stem cells that give rise to germinal cells have heterochromatin-rich nuclei with distinct nucleoli and scarce cytoplasm containing mainly free ribosomes and few mitochondria. The differentiating germinal cells undergo a growth, which is accompanied by an emergence of annulate lamellae and the nuage in their cytoplasm, a noticeable development of RER and Golgi apparatus and an increase in the number of mitochondria. The mitochondria form a large group at one of the cell poles. During differentiation, the nucleus and nucleolus of the germinal cell enlarge while the chromatin becomes gradually less condensed. The supporting tissue of the germinal mass is made up of cells connected by septate junctions. These supporting cells are distinctly different in cellular shape and nuclear ultrastructure. Their outgrowths form a tight meshwork housing stem cells, germinal cells and early cercarial embryos. The cytoplasm of the supporting cells in the mesh area is separated into fine parallel layers by labyrinthine narrow cavities communicating with the intercellular space. The supporting tissue contains differentiating and degenerating cells which indicates its renewal. The results of this ultrastructural study lend support to the hypothesis that the germinal cells of digeneans are germ line cells.
KeywordsSupporting Cell Germ Line Cell Germinal Cell Supporting Tissue Residual Body
This work was supported by the Russian Foundation for Basic Research (grant no 13-04-00875). The authors are deeply grateful to Mr. AE Tenison for his technical assistance.
- Ataev GL, Avanessjan AV, Loker ES, Dobrovolskij AA (2001a) The organization of the germinal material and dynamics of mother sporocyst reproduction in the genus Echinostoma (Trematoda: Echinostomatidae). Parazitologiya 35:307–319 (In Russian)Google Scholar
- Björkman N, Thorsell W (1964) On the ultrastructure of the ovary of the liver fluke (Fasciola hepatica L.). Z Parasitenkd 63:538–549Google Scholar
- Dobrovolskij AA, Galaktionov KV, Muhamedov GK, Sinha BK, Tihomirov IA (1983) Parthenogenetic generations of trematodes. Tr Leningr Obshestva Estestvoispytatelei 82:1–108 (in Russian)Google Scholar
- Dobrovolskij AA, Ataev GL (2003) The nature of reproduction of trematodes rediae and sporocysts. In: Combes C, Jourdane J (eds) Taxonomy ecology and evolution of metazoan parasites, vol I. PUP, Perpignan, pp 249–272Google Scholar
- Hori I (1992) Cytological approach to morphogenesis in the planarian blastema I. Cell behavior during blastema formation. J Submicrosc Cytol Pathol 24:75–84Google Scholar
- Isakova NP (2011) Germinal mass of the rediae of Trematoda. Parazitologiya 45:358–366 (In Russian)Google Scholar
- Køie M, Petersen ME (1988) A new annelid intermediate host (Lanassa nordenskioeldi Malmgren, 1866) (Polychaeta: Terebellidae) for Aporocotyle sp. and a new final host family (Pisces: Bothidae) for Aporocotyle simplex Odhner, 1900 (Digenea: Sanguinicolidae). J Parasitol 74:499–502CrossRefGoogle Scholar
- Morozova KN, Gubanova NV, Kiseleva EV (2005) Structural organization and possible functions of annulate lamellae. Tsitologiya 47:667–678 (In Russian)Google Scholar
- Podvyaznaya IM (1990) The morphology and ultrastructure of the female reproductive system of Prosthodendrium ascidia (Trematoda, Lecithodendriidae). Proc Zool Inst USSR Acad Sci 221:61–78 (in Russian)Google Scholar
- Podvyaznaya IM (2003) Ultrastructural studies of the female reproductive system in a parasite of bats Allassogonoporus amphoraeformis (Digenea: Allassogonoporidae). Parazitologiya 37:387–393 (in Russian)Google Scholar