Re-evaluation of the systematic positions of oxytrichid ciliates (Alveolata: Ciliophora: Hypotrichia) with multiple dorsal kinety fragmentation using morphological, morphogenetic, and multi-gene phylogenetic approaches

This study takes an integrative taxonomic approach, combining morphology, morphogenesis, and multi-gene phylogenetics, to investigate Korean populations of non-stylonychine oxytrichid ciliates previously assigned to Australocirrus and characterized by complex dorsal kinety fragmentation. Our comprehensive data reveal that these species represent four distinct genera: the redefined Australocirrus, Anteaustralocirrus gen. nov., Apoaustralocirrus gen. nov., and the resurrected Cyrtohymenides . We identify several morphological and morphogenetic characters of newly recognized generic significance that differentiate these taxa, including: (i) random multiple dorsal kinety 3 fragmentation along the anlage in Australocirrus; (ii) distinct undulating membranes patterns defined by specific curvature and crossing points (‘Anteaustralocirrus’, ‘Apoaustralocirrus’, and ‘Australocirrus’ patterns); (iii) the arrangement of transverse cirri, e.g. forming a slightly curved pseudorow in Cyrtohymenides; (iv) the number of dorsomarginal kineties (two in Anteaustralocirrus vs. at least three in others); (v) the presence/absence of specific cortical features, such as fibres surrounding dorsal bristles in Apoaustralocirrus and its phylogenetically related oxytrichid and neokeronopsid genera; and (vi) cyst morphology. Multi-gene phylogenetic analyses, incorporating a total of 36 newly obtained sequences (31 ribosomal DNA and five mitochondrial COI), robustly support the proposed generic assignments and highlight the taxonomic significance of these differentiating characters.