Identification of Sindiplozoon coreius (Monogenea, Diplozoidae) and morphological characteristics of the various...

Diplozoids are ectoparasites that mainly infect the gills of freshwater fish. While the life cycles of Eudiplozoon nipponicum (Goto, 1891) Khotenovsky, 1985 and some Paradiplozoon Achmerov, 1974 species are documented, Sindiplozoon Khotenovsky, 1981, development remains unclear. During a survey of fish parasites, diplozoids were collected from the predatory carp, Chanodichthys erythropterus Basilewsky, 1855, in the Lancang River and cultured Kanglang fish, Anabarilius graham Regan, 1908, in Kunming. Morphological and molecular methods confirmed all specimens as Sindiplozoon coreius Cao, 2022, and five developmental stages with their typical features were observed through morphological observations: oval egg with filament; ciliated oncomiracidium with hooks and one pair of clamps; diporpa with additional clamps; X-shaped juvenile with developing clamps; and adult with complete clamps and mature reproductive system. Morphometric analysis showed the central hook grew significantly during the transition from oncomiracidium to diporpa (p < 0.001). The buccal sucker, pharynx, and body length increased notably from juvenile to adult (p < 0.001). Clamps developed steadily throughout the life cycle, reaching maximum maturity at the adult stage. This is the first detailed description of S. coreius development, confirming species identity and expanding its known host range and distribution. Graphical Abstract.