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

Diplozoids are ectoparasites that mainly infect the gills of freshwater fish. While the life cycles of <i>Eudiplozoon nipponicum</i> (Goto, 1891) Khotenovsky, 1985 and some <i>Paradiplozoon</i> Achmerov, 1974 species are documented, <i>Sindiplozoon</i> Khotenovsky, 1981, development remains unclear. During a survey of fish parasites, diplozoids were collected from the predatory carp, <i>Chanodichthys erythropterus</i> Basilewsky, 1855, in the Lancang River and cultured Kanglang fish, <i>Anabarilius graham</i> Regan, 1908, in Kunming. Morphological and molecular methods confirmed all specimens as <i>Sindiplozoon coreius</i> 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 (<i>p</i> < 0.001). The buccal sucker, pharynx, and body length increased notably from juvenile to adult (<i>p</i> < 0.001). Clamps developed steadily throughout the life cycle, reaching maximum maturity at the adult stage. This is the first detailed description of <i>S. coreius</i> development, confirming species identity and expanding its known host range and distribution. <b>Graphical Abstract</b>.