Classification of the peritrich ciliate Opisthonecta matiensis (Martín-Cereceda et al. 1999) as Telotrochidium matiense nov. comb., based on new observations and SSU rDNA phylogeny

New observations on Opisthonecta matiensis Martín-Cereceda et al. [1999. Description of Opisthonecta matiensis n. sp. (Protozoa, Ciliophora), a new peritrich ciliate from wastewater. J. Eukaryot. Microbiol. 46, 283–289] especially the lack of an epistomial membrane, reveal that the species does not belong to the genus Opisthonecta, but to Telotrochidium, the other genus within the family Opisthonectidae Foissner, 1975. The contractile vacuole and the cytopyge are on the dorsal wall of the vestibulum and the trochal band is limited distally and proximally by rows of narrowly spaced pellicular pores. Thus the species is redefined as Telotrochidium matiense nov. comb. The morphological, cortical and nuclear events occurring during conjugation are illustrated, compared with those in other species, and phylogenetically discussed. Invariably, the microconjugants attach to and penetrate the lateral side of the macroconjugants. Nuclear processes are very similar to those reported from other peritrichs. The small subunit rRNA gene (SSU rDNA) is sequenced and the phylogeny within Opisthonectidae and peritrichs examined. T. matiense is more closely related to Epistylis (63% Maximum Parsimony (MP), 85% Maximum Likelihood (ML)) than to any other genus, while another representative of the family, viz., Opisthonecta henneguyi, is closely related to Vorticella microstoma, Astylozoon enriquesi and clone RT3n18 (100% MP, 100% ML). Morphology and gene sequences suggest that Telotrochidium and Opisthonecta have derived from different lineages of stalked peritrichs: Opisthonecta could have arisen from peritrichs with stalk myonemes, while Telotrochidium probably evolved from peritrichs without stalk myonemes.