Reproduction of Echinostoma caproni mother sporocysts (Trematoda)
G. L. Ataev
A. S. Tokmakova
Received: 12 February 2018 /Accepted: 14 May 2018
Springer-Verlag GmbH Germany, part of Springer Nature 2018
The localisation and the composition of germinal material in miracidia and mother sporocysts of Echinostoma caproni were
studied with the use of histological and electron microscopic methods. Germinal material in miracidia was localised in the
posterior body half and was represented by 3–4 undifferentiated cells and 5–7 germinal cells. Taken together, these cells are
referred to as the primordium of the germinal mass. In the mother sporocyst, germinal elements also form and develop in the
germinal mass, which is located caudally. It comprises undifferentiated cells and germinal cells as well as embryos of various
ages (up to the stage of 30–50 blastomeres). Germinal cells divide only by cleavage. New germinal cells are formed only from
undifferentiated cells, which can proliferate in the germinal mass and nowhere else. This indicates that the germinal mass is the
reproductive organ of E. caproni mother sporocyst.
Keywords Echinostoma caproni
Reproduction of rediae and sporocysts of trematodes remains
a debatable issue. Most researchers concur that embryos of
rediae and sporocysts originate from germinal cells (GC).
However, the nature of these cells is interpreted in several
According to the theory of metagenesis, the life cycle of
trematodes is an alternation of sexual and asexual generations
(Steenstrup 1842). The supporters of this theory are united in
thinking that rediae and sporocysts reproduce asexually but
disagree over the issue of what form their reproduction takes:
whether it is budding, polyembryony or development of em-
bryos from neoblasts. The prevailing idea is that reproduction
of rediae and sporocysts is internal budding and that the de-
velopment of buds is initiated by the division of diploid toti-
potent cells (Clark 1974).
According to the theory of heterogony, rediae and sporo-
cysts reproduce sexually and GC are parthenogenetic eggs
(Grobben 1882; Leuckart 1882; Sinitzin 1910, et al.). The
authors of this theory thought that parthenogenesis of rediae
and sporocysts was meiotic but subsequent attempts to find
any evidence of meiosis in GC have failed.
In a detailed review of reproduction of rediae and sporo-
cysts, Whitfield and Evans (1983) observed that evidence in
favour of parthenogenesis was lacking and concluded that
intramolluscan stages of trematodes reproduced asexually.
Their review became widely known; the hypothesis of meta-
genesis was accepted by many parasitologists, and discussions
about reproduction of rediae and sporocysts subsided.
However, there remained a possibility that rediae and spo-
rocysts might reproduce by ameiotic parthenogenesis (apo-
mixis). This view is shared by the modern supporters of the
theory of heterogony (Dobrovolskij and Ataev 2003;
Galaktionov and Dobrovolskij 2003;Ataev2017). In this pa-
per, we analysed the reproduction of mother sporocysts (MS)
of Echinostoma caproni in the light of this idea about the
nature of GC.
E. caproni is one of the most widely studied trematodes
(see Fried and Graczyk 2000; Fried and Toledo 2009). Various
aspects of MS development in this species have been investi-
gated such as the infection of the mollusc, the migration of
sporocysts and the dynamics of their growth and reproduction
as well as factors regulating these processes (Idris and Fried
1996; Ataev et al. 1997, 1998; Ataev and Coustau 1999).
Miracidia of E. caproni are a convenient model for the
study of MS reproduction because their GC never cleave
* G. L. Ataev
Laboratory of Experimental Zoology, Department of Zoology,
Faculty of Biology, Herzen State Pedagogical University of Russia,
Moyka River 48, St Petersburg, Russia 191186