Insight into the diversity and phylogeny of the ciliate family Lynchellidae (Alveolata: Ciliophora), with the establishment of a new genus and two new species

Abstract Two unusual algivorous ciliates, Paracoeloperix composita gen. nov., sp. nov. and Chlamydonella wangi sp. nov., were collected from marine habitats in China. Their morphology and molecular phylogeny were investigated using microscopical and ribosomal gene sequencing techniques. Paracoeloperix gen. nov. can be distinguished from its most closely related genus, Coeloperix, by its distinct trilinear oral ciliature and its small subunit ribosomal ribonucleic acid (SSU rRNA) gene sequence divergence. Paracoeloperix composita gen. nov., sp. nov. is characterized by having trilinear perioral kineties, a complete cross-striated band, finger-like tentacles on the ventral side, and anterior and left terminal fragments. Chlamydonella wangi sp. nov. differs from its congeners by having a reniform body, four or five contractile vacuoles, 17–19 somatic kineties, and 2.6%–8.3% SSU rDNA sequence dissimilarity. The systematic placements of the family Lynchellidae and the genus Paracoeloperix gen. nov. remain elusive owing to their low support values in phylogenetic trees and the unstable topology of these trees. Furthermore, the present study rejects the monophyly of the genus Chlamydonella because Chlamydonella wangi sp. nov. is closely related to Chlamydonellopsis calkinsi. Additionally, an illustrated identification key of Lynchellidae genera and a conjecture based on mapping between morphological features and the SSU rDNA tree are provided.