Phylogeny and systematic revision of the karyorelictid genus Remanella (Ciliophora, Karyorelictea) with descriptions of two new species

We present here the systematic relationships and taxonomy of some newly collected karyorelictid ciliates from the genus Remanella isolated from the intertidal zone in China. Three species were investigated using observation in vivo and silver staining methods, of which two new species were identified: R. macrostoma sp. nov. and R. achroma sp. nov. Small subunit (SSU) rRNA genes were sequenced for six species and phylogenetic analyses indicated that the genus Remanella is paraphyletic, with three Loxodes species nesting within it. The monophyly of Remanella, however, could not be rejected through the approximately unbiased (AU) test (p = 0.311 > 0.05) and therefore we considered Remanella to be a valid genus. Based on a critical review of the literature, the validity of all nominal species of Remanella was discussed. Remanella unirugosa and R. multicorpusculata were regarded as junior synonyms of R. rugosa and R. granulosa respectively. We also presented here an illustrated taxonomic key based on morphologic and morphometric characteristics and containing all Remanella species considered identifiable in this revision.