Morphology, Ontogenesis, and Multi‐Gene Phylogeny of the Type Species Cyrtohymena muscorum (Kahl, 1932) Foissner, 1989 (Alveolata, Ciliophora, Hypotricha)

ABSTRACT Members of the oxytrichid genus Cyrtohymena are characterised by a distinctive undulating membranes type, known as the Cyrtohymena pattern, featuring a strongly curved stichodyad paroral that forms a semicircle distally. Although the type species, Cyrtohymena muscorum , has been redescribed morphologically, its ontogenesis remains poorly understood due to missing data on key developmental stages. In addition, previous phylogenetic studies support that the genus is polyphyletic. In this study, we investigated the morphology and ontogenesis of C. muscorum using live observation, protargol impregnation, and scanning electron microscopy. Our detailed analysis clarified the origin of each frontal‐ventral‐transverse cirral anlage in both the proter and opisthe. Phylogenetic analyses based on multiple genes show that Cyrtohymena clusters with other species exhibiting a similar arrangement of transverse cirri, indicating that this feature carries a strong phylogenetic signal. A critical review of previous records suggests potential misidentifications and underestimation of species diversity within the group. The revised generic diagnosis indicates that several species currently assigned to Cyrtohymena may, in fact, belong to other genera.