Ultrastructural study of oogenesis in the acotylean Echinoplana celerrima, (Platyhelminthes, Polycladida)

Ultrastructure of the ovary and oogenesis in the flatworm Prosthiostomum siphunculus (Polycladida, Cotylea)

“…In polyclads, eggshell globules of five species have been described, including one cotylean, P. floridanus (Boyer, ) and four acotyleans: Notoplana alcinoi (Domenici et al, ), Pseudostylochus sp. (Ishida and Teshirogi, ), P. atomata (Liana and Litvaitis, ), and E. celerrima (Gammoudi et al, ). Typically, and also in the cotylean P. siphunculus studied here, an electron‐dense core is surrounded by a less dense, often granular cortex.…”

“…The basal lamina and the accessory cells (sometimes also referred to as somatic, follicular, or nurse cells) with their projections form a tunica, separating germinal cells from the rest of the parenchyma (Figures 1A, 1C, 2A-2C, 3A, 5B, 6A, and 6B), and leading to a sacular condition of the ovarian follicles (Rieger et al, 1991). Such a tunica was found in polyclads (Boyer, 1972;Liana and Litvaitis, 2009;Gammoudi et al, 2016a), in some prorhynchids (Falleni, 1997), proseriates (Sopott-Ehlers, 1986, rhabdocoels (Lucchesi , 1995;Falleni et al, 1998Falleni et al, , 2002Falleni et al, , 2005, macrostomids (Rieger et al, 1991), and triclads (Falleni et al, 2006(Falleni et al, , 2009. The basal lamina was not found in some other free-living flatworms like the marine triclad Sabussowia dioica (Tekaya et al, 1999), the freshwater triclad Dugesia sicula (Charni et al, 2010), and in prorhynchids (Falleni, 1997).…”

“…Interestingly, abortive oocytes already contain eggshell globules, which may be directly incorporated to growing oocytes. In the acotylean polyclad, E. celerrima were described as "degenerating oocytes" and in Macrostomum, abortive eggs have been described in the growth zone of the ovaries (Rieger et al, 1991;Gammoudi et al, 2016a).…”

“…Only relatively few representatives of flatworms with homocellular female gonads have been investigated to date, including macrostomids (Gremigni et al, 1987;Kuales et al, 2011) and polyclads (Domenici et al, 1975;Gremigni, 1983;Ishida and Teshirogi, 1986;Liana and Litvaitis, 2009;Gammoudi et al, 2016a).…”

“…As the germ cells mature, there is an accumulation of yolk and eggshell globules in their ooplasm. The eggshell globules migrate to the periphery in mature vitellogenic oocytes (Domenici et al, 1975;Liana and Litvaitis, 2009;Gammoudi et al, 2016a).…”