The class Karyorelictea, a unique assemblage of ciliates, is a key group in deciphering ciliate evolution history. However, the systematic relationships among members of this class remain poorly understood. Here we newly obtained eight small subunit (SSU) rDNA, 24 large subunit (LSU) rDNA, and 25 ITS1-5.8S-ITS2 sequences (covering 25 species, 10 genera and 4 out of 6 families) to analyze the phylogenetic relationships within Karyorelictea. Our results indicate that: (1) considering its unique morphology and early branching position in the SSU rDNA-based tree, the family Wilbertomorphidae represents a new taxon at order level, hence the new order Wilbertomorphida n. ord. is established; (2) all five families with available molecular information are monophyletic, as expected, and the orders Loxodida and Protostomatida show a closer relationship than with Protoheterotrichida; (3) in Trachelocercidae, the compound circumoral kineties is believed to be a plesiomorphic feature while the single circumoral kinety is synapomorphic; and (4) the freshwater genus Loxodes could be derived from the marine Remanella and both share most morphological features. Taken together, these muti-gene analyses provide further insights into the phylogeny of the diverse clades in Karyorelictea.
Keywords: Ciliates; ITS1-5.8S-ITS2; LSU rDNA; Phylogeny; SSU rDNA.
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