The present study investigates the morphologic and molecular characteristics of three Condylostoma species isolated from brackish and marine tropical habitats of China, including Condylostoma tropicum spec. nov., Condylostoma elongatum spec. nov. and Condylostoma curvum Burkovsky, 1970. The two new species have slender and elongated bodies with the posterior portion distinctly narrowed, forming long tails, thus they obviously differ from most congeners. In addition, Condylostoma tropicum spec. nov. is characterized by its small buccal cavity, single frontal cirrus, 26-33 somatic kineties, and moniliform macronucleus composed of 8-22 nodules. Condylostoma elongatum spec. nov. is distinguished by its huge body size (1000-1200μm long in vivo), the prominent buccal cavity, 5-7 frontal cirri and 37-43 somatic kineties. Condylostoma curvum is also reinvestigated in this paper using both protargol impregnation and molecular techniques. Phylogenetic analyses based on SSU rDNA sequence data indicate that the three organisms are located within the genus Condylostoma; the genus Condylostoma fails to form a monophyletic branch in both Maximum-likelihood tree and Bayesian inference analysis. Nonetheless, the AU test shows that the monophyly of Condylostoma could not be rejected.
Keywords: Condylostoma; Morphology; New species; Phylogeny.
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