A new morphological analysis of eggs and miracidia of Paratanaisia bragai (Digenea: Eucotylidae)

Paratanaisia bragai is a trematode that reaches sexual maturity in the kidney collecting ducts of domestic and wild birds, while the gastropods Subulina octona and Leptinaria unilamellata serve as its intermediate hosts. The morphology of P. bragai eggs is described here for the first time, using light, scanning and transmission electron microscopy. Embryonic eggs, obtained from adult worms collected from naturally infected definitive hosts, appeared elliptical, with an evident operculum, by all three microscopic techniques employed. Scanning electron microscopy revealed that the abopercular region presents a prominent U-shaped knob, which stands out from the egg surface. The thickness of the eggs, measured from ultrathin sections, were 0.34 ± 0.06 µm (0.29–0.50) at the ends and 0.31 ± 0.05 µm (0.24–0.36) in the middle region. The internal shell layer was more electron-dense and thinner than the middle layer, which comprised nearly the entire shell, while the external layer was less electron-dense and thinner than the internal layer. Rupture of the eggs, by the coverslip pressure, revealed the miracidia of P. bragai that was characterized by light and transmission electron microscopy.