Morphology and phylogeny of three trachelocercids ( Protozoa, Ciliophora, Karyorelictea), with description of two new species and insight into the evolution of the family Trachelocercidae.

Although trachelocercid ciliates are common in marine sandy intertidal zones, methodological difficulties mean that their biodiversity and evolutionary relationships have not been well documented. This paper investigates the morphology and infraciliature of two novel T rachelolophos and one rarely known form, T racheloraphis similis Raikov and Kovaleva, 1968, collected from the coastal waters of southern and eastern China. The small subunit ( SSU) r RNA gene sequences of two of the species are presented, allowing the phylogenetic position of the genus T rachelolophos to be revealed for the first time. Phylogenetic analyses based on SSU r RNA gene sequences indicate that T rachelolophos branches with K ovalevaia and forms a sister clade with the group including P rototrachelocerca, T rachelocerca and T racheloraphis. The monophyly of Trachelocerca is not rejected by the approximately unbiased ( AU) test ( P = 0.209, > 0.05) but that of T racheloraphis is rejected ( P = 3e-033, < 0.05). The newly sequenced genus T rachelolophos, and recent studies on the morphology and phylogeny of the family Trachelocercidae, suggest two new hypotheses about the evolution of the seven genera within Trachelocercidae, based on either infraciliature or molecular evidence. Both hypotheses suppose the compound circumoral kineties in the oral apparatus is a plesiomorphic feature while the single circumoral kinety is synapomorphic. More evidence is still needed, however, as to whether the closed circumoral kinety with no brosse feature in T rachelocerca is ancestral or secondarily reduced. © 2015 The Linnean Society of London [ABSTRACT FROM AUTHOR]