Abstract
Armophorean ciliates constitute an important component of microeukaryotic community in anaerobic or hypoxic environments. Yet, their diversity remains poorly known due to under-sampling or the scarcity of knowledge. In this study, three metopid ciliates, i.e.,
Metopus paraes
sp. n.,
Metopus spiculatus
sp. n., and
Metopus parapellitus
sp. n., collected from coastal sediments in Qingdao and Rizhao, China, were investigated using live observation, protargol staining, and molecular phylogenetic methods.
M. paraes
sp. n. can be distinguished by its long caudal cilia.
M. spiculatus
sp. n. resembles
M. vestitus
in many ways, but differs mainly in having a beak-like preoral dome end and a conspicuous tail. The most remarkable features of
M. parapellitus
sp. n. include an ovate body shape, caudal cilia located at the rear end and right posterior body, and an adoral zone that never extends onto the dorsal surface. Sequence divergences supported the species identification of these three species. Phylogenetic analyses confirmed that the
Metopus
is not monophyletic, and first revealed that all marine species of
Metopus
form a well-supported clade. The clustering of these marine forms with
M. es
(type species) is not rejected by the AU test, which infers that the marine clade represents the genus
Metopus
together with
M. es.