Body Surface Ultrastructure as a Main Morphological Criterion for Distinguishing Adult Trematode Metagonimus suifunensis

In the present study, the ultrastructure of the body surface of mature trematodes of <i>Metagonimus suifunensis</i> Shumenko et al., 2017 has been studied for the first time. It has been found that the tegumental spines on the surface of their bodies are very different from those in three other species of large trematodes of the genus <i>Metagonimus</i>: <i>M. yokogawai</i> Katsurada, 1912; <i>M. takahashii</i> Suzuki in Takahashi, 1929; and <i>M. miyatai</i> Saito et al., 1997. Since other morphological characteristics do not allow us to distinguish between these species, the ultrastructure of tegumental spines can be considered the only reliable morphological feature differentiating this trematode from other representatives of the genus. It has also been suggested that the shape of these spines may correlate with the parasite's ability to damage the host's intestinal tissue.