Molecular phylogeny of unculturable Kariorelictea (Alveolata Ciliophora)

Karyorelictea is a class of traditionally unculturable ciliates characterized by a non-dividing macronucleus. Their classification has been recently revised and morphological redescription of many species has been performed as well. On the contrary, molecular data of karyorelictean ciliates are largely underrepresented in public databases. In the present article we resumed and improved a method to characterize 18S rRNA gene sequences through direct amplification and sequencing of single cells. Using this approach, we characterized 12 different karyorelictean molecular operational taxonomic units (MOTUs: nine trachelocercids, one Geleia , one Remanella and one Loxodes ), most of which were also photo-recorded. These molecular data were used to reconstruct phylogenetic relationships among the three orders (Protostomatida, Loxodida and rotoheterotrichida) in which the class is traditionally subdivided. The most supported tree topology shows an association between orders Loxodida (Loxodes,Remanella) and Protoheterotrichida(Geleia ), in contrast with previous works associating orders Loxodida and Protostomatida (trachelocercids) on a morphological basis.