A study on the non-monophyletic genera Australothrix and Holostichides based on multigene and morphological analyses with a reexamination of type materials (Protozoa: Ciliophora).

• The two genera, Australothrix and Holostichides , are non-monophyletic. • Argyrophilic cytopharynx structure might be an apomorphy of hypotrichs. • A list of species with the argyrophilic cytopharynx structure is provided. • Further study is needed for the cryptic/sibling H. heterotypicus -like species. In a study of ciliate diversity, we collected two new species of the genera Australothrix and Holostichides. Based on nuclear ribosomal genes, our study shows that these two genera are genetically non-monophyletic. To clarify the issues of the non-monophyly, we reexamined type material of H. heterotypicus , H. terrae , and Birojimia soyaensis. Based on multigene and morphometric analyses, Australothrix and Holostichides are clearly non-monophyletic even in mitochondrial CO1 gene trees. The multigene analyses show a clade composed of A. lineae sp. nov., H. terrae , and B. soyaensis , suggesting that a cytopharynx with argyrophilic structures might be their synapomorphy. A list of species with this type of cytopharynx is provided for further studies to either accept or reject this hypothesis. Based on the reexamination, we discriminate the morphologically nearly identical (cryptic/sibling) species H. obliquocirratus sp. nov. from H. heterotypicus and they show significant genetic dissimilarities in the multigene trees. They showed only few morphological (non-quantitative) differences and thus distinguishing them morphologically needs careful investigation. [ABSTRACT FROM AUTHOR]