Taxonomy and phylogeny of Tunicothrix (Ciliophora, Stichotrichia), with the description of two novel species, Tunicothrix brachysticha n. sp. and Tunicothrix multinucleata n. sp., and the establishment of Parabirojimidae n. fam.

The morphology and molecular phylogeny of two novel urostylid ciliates, Tunicothrix brachysticha n. sp. and Tunicothrix multinucleata n. sp., were investigated using the techniques of living observation, protargol impregnation and small-subunit rRNA gene sequencing. Both species were found to be frequent in muddy-sand sediment but very rare in sandy sediment of the intertidal zone of Qingdao Bay, China. Tunicothrix brachysticha is about 90 × 30 µm in vivo, with a broadly clavate body shape, and is characterized by a rather short midventral row terminating at 40 % of the body length and a right marginal row 1 terminating at mid-body. Tunicothrix multinucleata is about 190 × 30 µm in vivo, and is characterized by a clavate body shape and the presence of 7-10 macronuclear nodules. Phylogenetic analyses showed that Tunicothrix clustered robustly with Parabirojimia, forming a clade that branches from the Urostylida core clade with high bootstrap values. Based on the morphological and molecular data, we establish a new family, Parabirojimidae n. fam., which comprises Parabirojimia and Tunicothrix and is distinguished by a unique, roughly T-shaped bipartite adoral zone of membranelles, three enlarged frontal cirri and a midventral complex with midventral pairs confined to the buccal field.