Abstract
The phylogeny of the oligotrich ciliates is currently a hot debate despite the availability of both morphological and molecular data. In the present paper, further small subunit rRNA (SS rRNA) genes were analyzed from the Genera
Omegastrombidium
and
Novistrombidium
, as well as from
Strombidium
, and combined with three new SS rRNA sequences from
Strombidium basimorphum, S. sulcatum
population QD-1, and
Novistrombidium testaceum
population GD. The phylogenetic positions of these organisms were inferred using Bayesian inference, Maximum Likelihood, and Maximum Parsimony methods. The main results are: (1) the SS rRNA gene sequence analyses match the recent findings about the molecular evolution of oligotrichs, indicating that the family Strombidiidae is paraphyletic; (2) the Genus
Omegastrombidium
is separated from the Genus
Strombidium
, as shown in recent cladistic analyses; (3) morphospecies in Genus
Novistrombidium
, based on similarity of somatic ciliature, are separated from each other in all topological trees, indicating that this genus could be a paraphyletic group; (4) the molecular data indicate a possibility of paraphyly for the genus
Strombidium
; and (5) the similarities of the SS rRNA gene of specimens identified as
S. sulcatum
and
S. inclinatum
are 99.8%–100%. However, present knowledge on the oligotrichs sensu stricto is still insufficient and further studies based on both molecular and other technologies are required.