Small-subunit rRNA Phylogenies Suggest That Epalxella antiquorum (penard, 1922) corliss, 1960 (ciliophora, odontostomatida) is a member of the plagyopylea.

The odontostomatid ciliates have remained a homogeneous order of ciliates since the 1930s when they were recognized as a monophyletic assemblage. Since that time they have been placed with the heterotrich ciliates, and more recently transferred as incertae sedis to the new "riboclass" class Armophorea. We were able to obtain the small subunit rRNA gene sequence of the odontostomatid Epalxella antiquorum (Penard, 1922) Corliss, 1960, collected from the meromictic alpine Lake Alat in Germany, in July 2005. An alignment with representatives of all 11 classes of ciliates unambiguously places the Epalxella sequence with other representatives of the class Plagiopylea with 100% support in both maximum likelihood and Bayesian analyses. Epalxella is the basal lineage with trimyemid and plagiopylid ciliates forming the two terminal sister clades. While this molecular support is strong and unambiguous, there are no obvious morphological features to unite these three clades. Thus, the class Plagiopylea must continue to be referred to as a "riboclass." Using the Epalxella sequence as a basal marker, we tentatively identified 20 environmental sequences to the terminal plagiopylean clades: eight to the genus Trimyema; four to the genus Plagiopyla; and eight to two new species, one of which might represent a new plagiopylean genus.