Morphological reports on two species of Dexiotricha (Ciliophora, Scuticociliatia), with a note on the phylogenetic position of the genus

Two Dexiotricha species (Dexiotricha elliptica nov. comb. and Dexiotricha cf. granulosa), respectively isolated from soil north-west of Riyadh, Saudi Arabia, and freshwater in Shanghai, eastern China, were investigated using standard methods. The species Loxocephalus ellipticus Kahl, 1931 is reclassified here in the genus Dexiotricha and was characterized mainly by constantly showing 16 somatic kineties, three post-oral kineties with the middle one shortened, a contractile vacuole located subcaudally with an excretory pore near the posterior end of somatic kinety 2 and single caudal cilia. A Dexiotricha granulosa-like organism having a subcaudally located contractile vacuole and fewer somatic kineties was designated D. cf. granulosa. The small-subunit rRNA gene (SSU rDNA) sequences of these two species were characterized and their phylogenetic positions based on SSU rDNA sequences were revealed by means of Bayesian inference and maximum-likelihood analysis. Phylogenetic analyses confirmed Dexiotricha as a monophyletic genus and supported its assignment to the order Loxocephalida. However, its family assignment remains unsupported.