Organization of Parthenogenetic and Hermaphroditic Generations of Trematodes

Description of embryonic development and ultrastructure in miracidia of Cardiocephaloides longicollis (Digenea, Strigeidae) in relation to active host finding strategy in a marine environment

“…Although the exact function of these glands is still unclear, it has been suggested that they play role in adhesion and penetration of the snail host. The lack of micrographs showing all nuclei simultaneously in the apical gland probably impeded to observe four nuclei as Galaktionov & Dobrovolskij () hypothesized for strigeids, as well as Pan () for S. mansoni , revealing only three instead.…”

“…The source of nutrients for developing embryos after the extrusion of the egg into the environment would be the nutritive reserves in the vitellocytes. The large number of vitellocytes found in families with actively infecting miracidia, such as Fasciolidae or Echinostomatidae (up to 30–40, according to Galaktionov & Dobrovolskij, ; 25‐31 in Echinostoma caproni , Schmidt, ) coincides with C. longicollis , whose immature eggs contain approximately 35 vitellocytes. Therefore, they form polylecithal eggs, which represent the plesiomorphic condition in parasitic flatworms (Neodemata) (Xylander, ).…”

“…Transmission stages have to be capable to detect a suitable molluscan host, ensuring larval viability and infectivity to establish in such a host. Miracidia show two different infection and transmission strategies: actively‐infecting miracidia hatch from the eggs in the environment and swim actively to localize and penetrate the molluscan host (e.g., Fasciolidae, Echinostomatidae, Philophthalmidae, Schistosomatidae), or eggs are swallowed by a suitable mollusc host and such passively infecting miracidia hatch in their intestine (e.g., Plagiorchiida, Hemiuroidea, Brachylaimoidea) (Galaktionov & Dobrovolskij, ). Eggs can either be fully embryonated (intrauterine development within adult parasite) and miracidia hatch immediately upon appropriate stimuli, or either following a maturation period in the external environment.…”

Description of Maritrema portucalensis sp. nov. (Digenea, Microphallidae) parasite of Carcinus maenas (Crustacea, Decapoda) from Aveiro estuary, Northern Portugal

“…Actually, in the course of metacercariae morphogenesis of digenean species belonging to the family Microphallidae, such progenetic development in all definitive systems, including the reproductive one, is described by several authors (Martorelli and Schuldt 1990, Saville and Irwin 1991, Galaktionov and Dobrovolskij 2003. Moreover, progenetic metacercariae are functionally and morphologically similar to adult forms in the definitive hosts, and are sometimes referred to as adults (Lefebvre and Poulin 2005).…”

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

“…If there are only two generations of parthenitae (mother and daughter sporocysts) in the group, the development of embryos in daughter sporocysts is suspended, while mature cercariae, that have not emerged before the drop of temperature, may die and resorb during the winter (our unpublished data). In self-sustaining groups of rediae/daughter sporocysts (the so-called microhemipopulations or self-sustaining infrapopulations -see Galaktionov et al, 2014Galaktionov et al, , 2015, the character of reproduction may change with the onset of the cold spell: instead of producing cercariae, rediae start to produce rediae of the next generation (Chowaniec, 1961;Bednarz, 1962;Kendall, 1965;Dinnic, Dinnic, 1964;Machkevskiy, 1982;Rusanov, Galaktionov, 1984;Korniychuk, 2008). For groups of rediae of Himasthla spp.…”