A population of Xu , 2008 , a small kiitrichid ciliate, was isolated from a brackish water sample in Jiaozhou Bay, Qingdao, northern China. After comparison of its morphology and infraciliature, it is believed that this morphotype should be assigned to the genus ; hence, a new combination is suggested, ( Xu , 2008 ) nov. comb. The small-subunit (SSU) rRNA gene sequence was determined in order to elucidate the phylogenetic position of this poorly known, ambiguous genus. The organism can be clearly separated from its congener, Kahl, 1932, by the extremely shortened ventral cirral rows in the posterior ends. Based on the data available, an improved diagnosis is given for the genus: marine Kiitrichidae with prominent buccal field; two highly developed undulating membranes; non-grouped, uniform cirral rows on both ventral and dorsal sides; enlarged transverse cirri present, which are the only differentiated cirri; marginal cirri not present; one short migratory row located posterior to buccal field; structure of dorsal kineties generally in pattern. The sequence of the SSU rRNA gene of differs by 13 % from that of . Molecular phylogenetic analyses (Bayesian inference, least squares, neighbour joining, maximum parsimony) indicate that together with , diverges at a deep level from all other spirotrichs. Its branching position is between Phacodiniidia and Licnophoridia. The results strongly support the distinct separation of the clade, which always branches basal to the Stichotrichia–Hypotrichia–Oligotrichia–Choreotrichia assemblage. These results also confirm the previous hypothesis that the group, long assumed to be a close relation to the euplotids, represents a taxon at subclass level within the spirotrichs.


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