Redescription of Atopospira galeata (Kahl, 1927) nov. comb. and A. violacea (Kahl, 1926) nov. comb. with redefinition of Atopospira Jankowski, 1964 nov. stat. and Brachonella Jankowski, 1964 (Ciliophora, Armophorida)

Bit by bit toward the diversity of metopids: Description of the genus Pidimetopus n. gen. (Ciliophora: Armophorea)

While metopids (Armophorea: Metopida) represent the most species-rich group of free-living anaerobic ciliates thriving in hypoxic environments, our understanding of their true diversity remains incomplete. Most metopid species are still characterized only morphologically. Particularly, the so-called IAC clade (named in the past after some of the taxa included, Idiometopus, Atopospira, and Clevelandellida), comprising free-living members as well as the endosymbiotic ones (order Clevelandellida), is in serious need of revision. In our study, we establish a new free-living genus in the IAC clade, Pidimetopus n. gen., with descriptions of two new species, P. nanus n. sp., and P. permonicus n. sp., using up-to-date molecular and morphologic methods. The genus is characterized by small cells (up to 75 μm long), not more than 10 adoral membranelles and eight somatic kineties, and usually, four long caudal cilia that can stiffen. In addition to morphologic and molecular characterizations, we also conducted a statistical morphotype analysis of the polymorphic species P. nanus n. sp. We discuss the relevance of the earlier morphologically described species Metopus minor as a putative collective taxon for several small metopids less than 50 μm long.

Morphology, morphogenesis, and molecular characterization of Castula specialis sp. nov. (Ciliophora, Armophorea, Metopida)

The morphology, morphogenesis, and molecular phylogeny of a new metopid ciliate, Castula specialis sp. nov., comprising three strains from geographically distant (China, Mexico, Czech Republic) anoxic freshwater habitats, were studied based on microscopic observation of live and protargol-stained specimens as well as SSU rRNA gene sequence data. The new species is characterized as follows: size in vivo 105-220 × 25-70 μm, body oblong to elongated ellipsoidal and asymmetrical; preoral dome distinctly projecting beyond the body; 32-46 adoral membranelles; 31-52 somatic kineties; and 4-7 setae. This study brings the first morphogenetic investigation of a member of the genus Castula. The morphogenesis of the type population (China) of the new species proceeds as in Metopus spp. comprising drastic changes in body shape and a pleurotelokinetal stomatogenesis; however, the main difference is the origin of the opisthe's paroral membrane that derives from all perizonal rows and some adjacent dome kineties. Phylogenetically, the genus Castula is paraphyletic.

Morphology and phylogenetic position of three anaerobic ciliates from the classes Odontostomatea and Muranotrichea (Ciliophora)

The diversity of the classes Odontostomatea and Muranotrichea, which contain solely obligate anaerobes, is poorly understood. We studied two populations of Mylestoma sp., one of Saprodinium dentatum (Odontostomatea), two of Muranothrix felix sp. nov., and one of Muranothrix sp. (Muranotrichea) employing live observation, protargol impregnation, scanning electron microscopy, and 18S rRNA gene sequencing. Conspecificity of Mylestoma sp., described here, with a previously described species of this genus cannot be excluded since no species have been studied with modern methods. Phylogenetically, the genus Mylestoma is closely related to the odontostomatid Discomorphella pedroeneasi, although the phylogenetic position of class Odontostomatea itself remains unresolved. The newly described muranotrichean species, Muranothrix felix sp. nov., is morphologically similar to M. gubernata but can be distinguished by its fewer macronuclear nodules and fewer adoral membranelles; moreover, it is clearly distinguished from M. gubernata by its 18S rRNA gene sequence. Another population, designated here as Muranothrix sp., most likely represents a separate species.

Diversity and Phylogenetic Position of Bothrostoma Stokes, 1887 (Ciliophora: Metopida), with Description of Four New Species

Bothrostoma is a genus of anaerobic ciliates in family Metopidae comprising four species, all described based solely on the morphology of living and fixed cells. Unlike other metopids, cells of Bothrostoma are not twisted anteriorly, have a flattened preoral dome, a very prominent sail-like paroral membrane, and an adoral zone of distinctive, very narrow, curved membranelles confined to a wide, non-spiraling peristome on the ventral side. We examined 20 populations of Bothrostoma from hypoxic freshwater sediments. We provide morphological characterization and 18S rRNA gene sequences of four new species, namely B. bimicronucleatum sp. nov., B. boreale sp. nov., B. kovalyovi sp. nov., and B. robustum sp. nov., as well as B. undulans (type species), B. nasutum, and B. ovale comb. nov. (original combination Metopus undulans var. ovalis Kahl, 1932). Except for B. nasutum, Bothrostoma species show low genetic variability among geographically distant populations. Intraspecific phenotypic variability might be driven by environmental conditions. In phylogenetic analyses, Bothrostoma is not closely related to Metopus sensu stricto and forms a moderately supported clade with Planometopus, here referred to as BoPl clade. The anterior axial torsion of the body, typical of other Metopidae, appears to have been lost in the last common ancestor of the BoPl clade.

Morphology and phylogeny of two anaerobic freshwater ciliates: Brachonella comma sp. nov. and the widely-distributed but little-known caenomorphid, Ludio parvulus Penard, 1922

Hypoxic, sulfidic freshwater sediments typically support a diffuse consortium of distinctive ciliated protists, including caenomorphids, metopids, and odontostomatids among others. A recent resurgence of interest in these important members of sapropelic food webs has resulted in the description of many new species and an effort, still in its infancy, to characterize them from a morphologic, molecular, and metabolic standpoint and to determine their phylogenetic relationships. Their seemingly invariable association with prokaryotic endosymbionts and, less commonly, ectosymbionts, has become a focus for many researchers. In this report, based on morphologic and molecular data we describe a Brachonella species (Ciliophora, Metopida) new to science and analyze its phylogeny. We also provide a morphologic and molecular characterization of the smallest representative of the Caenomorphidae Poche, 1913, Ludio parvulus Penard, 1922. The phylogenetic analysis confirms the inclusion of this species in the Caenomorphidae.

Description of Three New Genera of Metopidae (Metopida, Ciliophora): Pileometopus gen. nov., Castula gen. nov., and Longitaenia gen. nov., with Notes on the Phylogeny and Cryptic Diversity of Metopid Ciliates

We report the discovery of three new species of freshwater metopid ciliates, Pileometopus lynni gen. et sp. nov., Castula flexibilis gen. et sp. nov., and Longitaenia australis gen. et sp. nov. Based on morphologic features and the 18S rRNA gene phylogeny, we transfer two known species of Metopus to the new genus Castula, as C. fusca (Kahl, 1927) comb. nov. and C. setosa (Kahl, 1927) comb. nov. and another known species is herein transferred to the new genus Longitaenia, as L. gibba (Kahl, 1927) comb. nov. Pileometopus is characterized by a turbinate body shape, a dorsal field of densely spaced dikinetids, a bipartite paroral membrane, and long caudal cilia. A distinctive morphologic feature of Castula species is long setae arising over the posterior third of the body (as opposed to a terminal tuft). Longitaenia spp. are characterized by an equatorial cytostome and long perizonal ciliary stripe relative to the cell length. Based on phylogenetic analyses of 18S rRNA gene sequences, we identify and briefly discuss strongly supported clades and intraspecific genetic polymorphism within the order Metopida.

A Proposed Timescale for the Evolution of Armophorean Ciliates: Clevelandellids Diversify More Rapidly Than Metopids

Members of the class Armophorea occur in microaerophilic and anaerobic habitats, including the digestive tract of invertebrates and vertebrates. Phylogenetic kinships of metopid and clevelandellid armophoreans conflict with traditional morphology-based classifications. To reconcile their relationships and understand their morphological evolution and diversification, we utilized the molecular clock theory as well as information contained in the estimated time trees and morphology of extant taxa. The radiation of the last common ancestor of metopids and clevelandellids very likely occurred during the Paleozoic and crown diversification of the endosymbiotic clevelandellids dates back to the Mesozoic. According to diversification analyses, endosymbiotic clevelandellids have higher net diversification rates than predominantly free-living metopids. Their cladogenic success was very likely associated with sharply isolated ecological niches constituted by their hosts. Conflicts between traditional classifications and molecular phylogenies of metopids and clevelandellids very likely come from processes, leading to further diversification without extinction of ancestral lineages as well as from morphological plesiomorphies incorrectly classified as apomorphies. Our study thus suggests that diversification processes and reconstruction of ancestral morphologies improve the understanding of paraphyly which occurs in groups of organisms with an apparently long evolutionary history and when speciation prevails over extinction.