In this study, Frontonia leucas, Frontonia acuminata, Frontonia angusta, and Frontonia anatolica species isolated from aquatic environments of Van in Turkey were investigated in detail using morphological, morphometrical, and molecular methods. Although there were minor differences, the Frontonia populations were morphologically similar to the other previously reported populations of the 4 species. Frontonia leucas differed from the other populations by the following combination of characters: about 200 somatic and only 3 vestibular kineties, and a single micronucleus. The Turkish population of Frontonia acuminata had just 4 vestibular kineties and the large micronucleus was always located to the anterior of the carrot-shaped macronucleus. The ratio of the oral apparey size to the cell size of Frontonia angusta in this study was about 18%, with 3 vestibular kineties, and 1 excretory pore. Phylogenetic trees based on small-subunit rRNA gene sequences were constructed using Bayesian inference and maximum-likelihood. Frontonia anatolica was more closely related to Apofrontonia dohrni and Paramecium spp. than to its congeners, while F. acuminata, like F. terricola, was also more closely related to the family Stokesiidae. The results indicated that Frontonia is a non-monophyletic genus consisting of 3 groups. We presented the systematic relationships of the genera and families of Peniculida with new data of genus Frontonia herein.