Morphogenesis of the anaerobic ciliate Tropidoatractus levanderi (Ciliophora, Armophorea, Metopida), with notes on conjugation and molecular phylogeny

Tropidoatractidae, a recently established anaerobic family of metopid ciliates, have not yet been examined from a morphogenetic perspective. In this study, the interphase morphology, morphogenesis during binary fission, and body and certain nuclear changes during conjugation were investigated in a Chinese population of Tropidoatractus levanderi Rotterová et al., 2018 using the protargol impregnation method. The main findings are as follows: (1) the Chinese population closely resembles Czech and Brazilian populations, with the exception of a diplostichomonad type of paroral membrane, a feature previously overlooked; (2) divisional morphogenesis follows the metopid mode, providing further evidence for conserved cell division patterns within metopids, and (3) conjugation is of the total isogamontic type, a rare phenomenon among ciliates. Additionally, 18S rRNA gene sequence comparison and phylogenetic analyses were conducted to complement the morphological observations.