A new ciliate Urosomoida sp. n. (Ciliophora, Sporadotrichida, Oxytrichidae) from King George Island, Antarctica

Abstract

Ciliate, a unicellular eukaryote is an important component playing a intermediate trophic role between bacteria and multicellular eukaryotes in ecosystems. However, the Antarctic ciliate has been less considered and has sparsely investigated so far. In this study, a new "non-oxytrichid Dorsomarginalia" ciliate, Urosomoida sp. n. was discovered from freshwater near the King George Island, Antarctica using morphological, morphometrical, and molecular analyses. Morphology of U. sp. n. is characterized as follows: body shape slender to elongated; cortical granules spherical and colorless, groups of granules formed patchy distribution; ring-shaped structures scattered in cytoplasm; 27？30 adoral membranelles with undulating membranes in Oxytricha pattern; usually 17 frontal-ventral-transverse (FVT) cirri composed of 8 frontal, 3 postal ventral, 2 pretransverse ventral and 4 transverse cirri; 1 right and 1 left marginal rows; 3 dorsal kineties with 1 dorsomarginal row, 3 caudal cirri; 1 micronucleus between 2 macronuclear nodules. This new species mainly differs from other congeners by the combination of following morphological features: a micronucleus, cortical granules, and ciliatures (e.g., adoral membranelles, FVT cirri). Urosomoida sp. n. shows a nucleotide similarity of 97.3% with U. agilis, a type species of this genus, in the SSU rDNA sequences. Molecular phylogeny shows a non-monophyletic relationship among Urosomoida species and emphasizes the need for further morphogenetic studies of this genus and other related species.