The fine structure of the germinal mass, brood cavity and birth canal of the rediae of the monoxenous hemiuroid digeneanBunocotyle progeneticaChabaud & Buttner, 1959

Abstract

Bunocotyle progenetica is a hemiuroid digenean whose sexual adults become fully developed and lay their eggs inside the rediae in the molluscan host. In this study, the fine structure of the germinal mass, brood cavity and birth canal in the B. progenetica rediae was examined using transmission electron and confocal microscopy. The large germinal mass attached to the body wall has a cellular composition typical for this organ. The characteristic traits of this germinal mass are weakly developed supporting tissue and the presence of deep lacunae opening into the brood cavity. These lacunae presumably participate in feeding the deeply lying embryos and facilitate their release into the brood cavity. The germinal mass is also characterized by intensive degeneration of cellular elements, which may represent a mechanism controlling the offspring number, limited in this species by the size of the redial brood cavity. The brood-cavity lining consists of flattened cells bearing lamellar projections and is connected anteriorly with the epithelium of the birth canal. The brood-cavity musculature, which is well developed in other hemiuroid digeneans, is significantly reduced in B. progenetica, most likely because their cystophorous cercariae remain inside the rediae, removing the need for muscle contractions pushing them through the brood cavity. The birth canal comprises three regions distinguished by the structure of the lining and muscle arrangement. The comparison of rediae of B. progenetica with parthenitae of other digeneans has shown that the organization of the redial reproductive apparatus in this species may have been influenced by life-cycle modification.

Reproductive organs of trematode parthenitae during the cold season: an ultrastructural analysis using evidence from rediae of Bunocotyle progenetica (Markowski, 1936) (Digenea, Hemiuroidea)

“…The germinal mass of rediae of B. progenetica is attached to the body wall. Its ultrastructural organisation in the period of active functioning (in summer) was described in our earlier study (Podvyaznaya et al, 2019). We have shown that the germinal mass, the brood cavity of the redia and its birth canal opening with a birth pore on the outer surface of the parthenita, are elements of a welldeveloped integrated reproductive apparatus, in which the germinal mass is a functional equivalent of the gonad and all the other structures mentioned above play the role of efferent ducts.…”

“…Once their development is completed, fully formed cercariae or young parthenitae leave the mother organism through a birth pore or local ruptures of the body wall. Recently, we conducted the first ultrastructural studies of germinal masses in parthenitae of different morphotypes (sporocysts with modular organisation, rediae of different types) in species from phylogenetically distant trematode families (Podvyaznaya, 2007;, 2018Podvyaznaya et al, 2019). These investigations have confirmed the conclusion about a uniform cellular composition of the germinal masses across different digenean groups.…”

“…Infected molluscs were collected in hydrological winter (March) from under the ice at a temperature of near-sediment water of -1.5-1 °C. The ultrastructural study of the germinal masses and the brood cavity of "winter" rediae revealed substantial differences from their "summer" state described in Podvyaznaya et al (2019). The mitotic activity in the "winter" germinal masses decreased considerably but did not cease completely.…”

“…Our data suggest that a traditional view that the functional activity of trematode parthenitae stops completely in winter should be reconsidered. How to cite this article: Galaktionov K.V., Podvyaznaya I.M. 2019.…”

“…Зараженных моллюсков собирали в период гидрологической зимы (март) из-подо льда при температуре пригрунтовой воды -1.5-1 °C. Ультраструктурное исследование герминальных масс и выводковой полости «зимних» редий выявило значимые различия от их «летнего» состояния, описанного нами ранее (Podvyaznaya et al, 2019). Существенно ослабевает, но не прекращается, митотическая активность внутри герминальной массы.…”