A review of morphogenesis in hypotrichous ciliates (Ciliophora, Hypotricha): recent progress from the OUC-group

The study of ciliate morphogenesis provides crucial insights into the eukaryotic cell differentiation and organelle reorganization mechanisms. The morphogenetic patterns of ciliates also provide taxonomically diagnostic characters for species delimitation, higher-level classification, and phylogenetic inference. In collaboration with various international and domestic colleagues, the Ocean University of China (OUC) group's morphogenetic research has been published in 76 papers over the last decade. For the subclass Hypotrichia, the OUC group has investigated approximately 78 species representing 20 families (including seven species with unresolved familial classification) and 57 genera since 2016. Among them, three families, 17 genera, and 64 species were morphogenetically reported for the first time. Furthermore, morphogenesis was redescribed in detail for six genera and 15 species, with important additional information on their binary fission. Based on newly acquired morphological, morphogenetic, and phylogenetic data, four new families, ten new genera, and 42 new species were described. In addition, the investigations have revealed numerous novel morphogenetic phenomena, while simultaneously stimulating the proposition of innovative theoretical frameworks and testable evolutionary hypotheses. These advancements have significantly refined our understanding of the phylogenetic relationships of hypotrichs, enabling comprehensive reassessments of taxonomic positions across many ciliate lineages.