Morphology and SSU rRNA gene-based phylogeny of two marine Euplotes species, E. orientalis spec. nov. and E. raikovi Agamaliev, 1966 (Ciliophora, Euplotida)

The living morphology, infraciliature and silverline system of two small marine Euplotes species, E. orientalis spec. nov. and E. raikovi Agamaliev, 1966, isolated from a sandy beach near Qingdao, China, were investigated. Euplotes orientalis is characterized by a combination of features including their small size (35-45 μm long), five or six conspicuous dorsal ridges, two cilia-free basal plaques, eight normal-sized frontoventral cirri (FVC), and a double-patella-I type of silverline system. Euplotes raikovi is redescribed based on a Chinese population and includes the first detailed description of its morphology in vivo. It can be recognized by having one highly reduced and seven normal-sized frontoventral cirri, a single marginal cirrus, and a double-patella-I type of silverline system. For both species the small subunit rRNA (SSU rRNA) gene sequence was determined. Phylogenetic analyses based on these data indicate that E. orientalis is most closely related to E. plicatum and E. bisulcatus, whereas E. raikovi clusters with its conspecific strains, close to E. nobilii and E. elegans.