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Oligotrich ciliates are common marine microplankters, but their biodiversity and evolutionary relationships have not been well-documented. Morphological descriptions and small subunit rRNA gene sequences of two new species representing two new strombidiid genera, Sinistrostrombidium cupiformum gen. nov., sp. nov. and Antestrombidium agathae gen. nov., sp. nov. are presented, and their taxonomy and molecular phylogeny are analyzed. Sinistrostrombidium gen. nov. is characterized by a sinistrally spiraled girdle kinety and a longitudinal ventral kinety. Antestrombidium gen. nov. is distinguished by tripartite somatic kineties (circular and ventral kineties plus dextrally spiraled girdle kinety). Sinistrostrombidium and Antestrombidium branched separately from one another in phylogenetic trees, clustering with different clades of strombidiids. The new genera added to the diversities of ciliary patterns and small subunit rRNA gene sequences in strombidiids leads to presentation of a new hypothesis about evolution of the 12 known strombidiid genera, based on ciliary pattern and partly supported by molecular evidence. In addition, our new morphological and molecular analyses support establishment of a new order Lynnellida ord. nov., characterized by an open adoral zone of membranelles without differentiation of anterior and ventral membranelles, for Lynnella, but we remain unable to assign the genus to a subclass with confidence.

Haptorian ciliates in the closely similar genera Kentrophyllum and Epiphyllum possess a unique pattern of ciliature and are distinguished from one another only by the presence or absence of cytoplasmic spines projecting from the margin of the cell. Phylogenetic analyses based on SSU rDNA sequences of three new samples from coastal habitats in China revealed that species in the two genera clustered together indiscriminately (i.e. forms of neither genus clustered into an independent clade) as a maximally supported, monophyletic clade that branches basally to all other clades in the order Pleurostomatida and is strongly divergent from other members of the family in which the genera have been placed. As a result, we propose that Epiphyllum be synonymized with Kentrophyllum and that a new family Kentrophyllidae fam. n. be established for the genus. We hypothesize that the two-sutures of Kentrophyllum is a plesiomorphy within the Pleurostomatida and the unique peripheral kinety might represent an autapomorphy of Kentrophyllum. In addition, we provide a taxonomic revision of Kentrophyllum including description of three new species (K. bispinum sp. n., K. strumosum sp. n., and K. qingdaoense sp. n.), redescription of K. verrucosum (Stokes, 1893) Petz et al., 1995, and three new combinations (K. soliforme (Fauré-Fremiet, 1908) comb. n., K. hohuensis (Wang and Nie, 1933) comb. n. and K. shenzhenense (Pan et al., 2010) comb. n.). The surface ultrastructure of the genus Kentrophyllum is recorded for the first time. And a key to all known species of Kentrophyllum was also suggested.

Tachysoma pellionellum Stokes, 1887, a freshwater ciliate isolated from Stone Mountain State Park, North Carolina, was studied in vivo and after staining with protargol. The population was characterized mainly by having the typical 18 frontal-ventral-transverse cirri; posterior ends of left and right marginal rows not confluent; five dorsal kineties and one dorsomarginal kinety; two macronuclear nodules near left cell margin with one or two micronuclei between them; contractile vacuole located at mid-body near left margin. Morphogenesis is characterized as follows: (1) in the proter, the parental adoral zone of membranelles is retained completely; (2) 18 frontal-ventral-transverse cirri are derived from the anlage of the undulating membrane and the five streaks of the frontal-ventral-transverse anlagen; (3) marginal rows develop intrakinetally; (4) anlagen of dorsal kineties 1, 2 and 4 develop in the parental structure and anlagen of dorsal kineties 2 and 4 fragment in the posterior region forming anlagen of dorsal kineties 3 and 5; (5) only one dorsomarginal kinety formed; (6) the two macronuclear nodules fuse into a single mass, which then divides. Phylogenetic analyses based on sequences of the gene coding for SSU RNA revealed a close relationship between T. pellionellum and the Oxytricha clade, both of which grouped with Kleinstyla dorsicirrata and Heterourosomoida lanceolata.

Vorticella includes more than 100 currently recognized species and represents one of the most taxonomically challenging genera of ciliates. Molecular phylogenetic analysis of Vorticella has been performed so far with only sequences coding for small subunit ribosomal RNA (SSU rRNA); only a few of its species have been investigated using other genetic markers owing to a lack of similar sequences for comparison. Consequently, phylogenetic relationships within the genus remain unclear, and molecular discrimination between morphospecies is often difficult because most regions of the SSU rRNA gene are too highly conserved to be helpful. In this paper, we move molecular systematics for this group of ciliates to the infrageneric level by sequencing additional molecular markers—fast-evolving internal transcribed spacer (ITS) regions—in a broad sample of 66 individual samples of 28 morphospecies of Vorticella collected from Asia, North America and Europe. Our phylogenies all featured two strongly supported, highly divergent, paraphyletic clades (I, II) comprising the morphologically defined genus Vorticella. Three major lineages made up clade I, with a relatively well-resolved branching order in each one. The marked divergence of clade II from clade I confirms that the former should be recognized as a separate taxonomic unit as indicated by SSU rRNA phylogenies. We made the first attempt to elucidate relationships between species in clade II using both morphological and multi-gene approaches, and our data supported a close relationship between some morphospecies of Vorticella and Opisthonecta, indicating that relationships between species in the clade are far more complex than would be expected from their morphology. Different patterns of helix III of ITS2 secondary structure were clearly specific to clades and subclades of Vorticella and, therefore, may prove useful for resolving phylogenetic relationships in other groups of ciliates.

The role of biotic interactions in shaping the distribution and abundance of species should be particularly pronounced in symbionts. Indeed, symbionts have a dual niche composed of traits of their individual hosts and the abiotic environment external to the host, and often combine active dispersal at finer scales with host‐mediated dispersal at broader scales. The biotic complexity in the determinants of species distribution and abundance should be even more pronounced for hyper symbionts (symbionts of other symbionts). We use a chain of symbiosis to explore the relative influence of nested biotic interactions and the abiotic environment on occupancy and abundance of a hypersymbiont. Our empirical system is the epibiont ciliate Lagenophrys discoidea, which attaches to an ostracod that is itself ectosymbiotic on crayfish (the basal host). We applied multimodel selection and variance partitioning for GLMM to assess the relative importance of (a) traits of symbiotic hosts (ostracod sex and abundance), (b) traits of basal hosts (crayfish body weight, abundance and intermoult stage), (c) the abiotic environment (water chemistry and climate) and (d) geospatial autocorrelation patterns (capturing potential effects of crayfish dispersal among localities). Our models explained about half of the variation in prevalence and abundance of the hypersymbiont. Variation in prevalence was partly explained, in decreasing order of importance (18%–4%) by shared effects of symbiotic host traits and the abiotic environment, pure fixed effects of symbiotic hosts, abiotic environment and geospatial patterns (traits of basal hosts were not relevant). Hypersymbiont abundance was most strongly explained by random effects of host traits (mainly the symbiotic host), in addition to weaker fixed effects (mostly abiotic environment). Our results highlight the major role of the interplay between abundance of symbiotic hosts and water physico‐chemistry in regulating populations of a hypersymbiotic ciliate, which is likely critical for dispersal dynamics, availability of attachment resources and suitability of on‐host living conditions for the ciliate. We also found moderate signal of regulation by the basal host, for which we propose three mechanisms: (a) modulation of microhabitat suitability (crayfish‐created water currents); (b) concentration of symbiotic hosts within crayfish; and (c) dispersal mediated by crayfish. This article examines factors that regulate populations of a hypersymbiont (symbiont of a symbiont) that lives exposed to the water from which it obtains food. The authors provide the first evidence that the hypersymbiotic ciliate's ostracod host and the ostracod's crayfish host together with water physico‐chemistry regulate populations of the ciliate.

Oligotrich ciliates are common marine microplankters, but their biodiversity and evolutionary relationships have not been well-documented. Morphological descriptions and small subunit rRNA gene sequences of two new species representing two new strombidiid genera, Sinistrostrombidium cupiformum gen. nov., sp. nov. and Antestrombidium agathae gen. nov., sp. nov. are presented, and their taxonomy and molecular phylogeny are analyzed. Sinistrostrombidium gen. nov. is characterized by a sinistrally spiraled girdle kinety and a longitudinal ventral kinety. Antestrombidium gen. nov. is distinguished by tripartite somatic kineties (circular and ventral kineties plus dextrally spiraled girdle kinety). Sinistrostrombidium and Antestrombidium branched separately from one another in phylogenetic trees, clustering with different clades of strombidiids. The new genera added to the diversities of ciliary patterns and small subunit rRNA gene sequences in strombidiids leads to presentation of a new hypothesis about evolution of the 12 known strombidiid genera, based on ciliary pattern and partly supported by molecular evidence. In addition, our new morphological and molecular analyses support establishment of a new order Lynnellida ord. nov., characterized by an open adoral zone of membranelles without differentiation of anterior and ventral membranelles, for Lynnella, but we remain unable to assign the genus to a subclass with confidence.

Haptorian ciliates in the closely similar genera Kentrophyllum and Epiphyllum possess a unique pattern of ciliature and are distinguished from one another only by the presence or absence of cytoplasmic spines projecting from the margin of the cell. Phylogenetic analyses based on SSU rDNA sequences of three new samples from coastal habitats in China revealed that species in the two genera clustered together indiscriminately (i.e. forms of neither genus clustered into an independent clade) as a maximally supported, monophyletic clade that branches basally to all other clades in the order Pleurostomatida and is strongly divergent from other members of the family in which the genera have been placed. As a result, we propose that Epiphyllum be synonymized with Kentrophyllum and that a new family Kentrophyllidae fam. n. be established for the genus. We hypothesize that the two-sutures of Kentrophyllum is a plesiomorphy within the Pleurostomatida and the unique peripheral kinety might represent an autapomorphy of Kentrophyllum. In addition, we provide a taxonomic revision of Kentrophyllum including description of three new species (K. bispinum sp. n., K. strumosum sp. n., and K. qingdaoense sp. n.), redescription of K. verrucosum (Stokes, 1893) Petz et al., 1995, and three new combinations (K. soliforme (Faure-Fremiet, 1908) comb. n., K. hohuensis (Wang and Nie, 1933) comb. n. and K. shenzhenense (Pan et al., 2010) comb. n.). The surface ultrastructure of the genus Kentrophyllum is recorded for the first time. And a key to all known species of Kentrophyllum was also suggested.

Free-swimming trophonts of a sessiline peritrich ciliate were discovered in plankton samples from the Rhode River, Maryland, and main-stem Chesapeake Bay. Cultures revealed that the species comprises both free trophonts that swim with their peristomial cilia and sessile trophonts that attach to substrates with a contractile, helically-twisted stalk. Trophonts with a short, rigid stalk or no definite stalk also were seen in culture. Binary fission of free-swimming trophonts usually produced a pair of trophonts attached scopula to scopula by a short, rigid stalk. These persisted for some time as distinctive, spinning doublets before their stalks broke and they separated. Binary fission of free-swimming trophonts also yielded trophont-telotroch pairs that stayed together for only a short time. Telotrochs from these pairs were presumably the source of attached trophonts. Conjugation occurred in both free and attached trophonts. Formation of microconjugants involved at least 2 successive divisions of a trophont. Possession of a helically-twisted, contractile stalk placed the peritrich in the family Vorticellidae, but its unique combination of life-cycle stages marks it as a new genus and species, Planeticovorticella finleyi. The morphology and life cycle of P. finleyi raise questions about the present classification of sessiline peritrichs and suggest that it may be at least partly artificial. Stalkless planktonic peritrichs that swim with their oral cilia as do trophonts of P. finleyi may have evolved from sessile ancestors by an alteration in the life cycle that created unstable clusters of trophonts on a single parental stalk. Free-swimming trophonts would originate from breakup of these clusters.

Lagenophrys labiata, a poorly known ectocommensal of freshwater amphipods, was rediscovered and is redescribed. Lagenophrys wallengreni, an ectocommensal of freshwater ostracods, was originally a junior homonym of L. labiata. Lagenophrys wallengreni was discovered to be L. discoidea, another poorly known species, and is redescribed under that name. Lagenophrys patina, an ectocommensal of freshwater amphipods misidentified in the literature as L. labiata, was rediscovered and is redescribed. A second species of Lagenophrys misidentified as L. labiata occurs on hypogean amphipods. It was found to be new and is described as L. stygia n. sp. Lagenophrys labiata possesses a prominent, crescent-shaped bulge anteriad of the lorica aperture, which clearly distinguishes it from the other three species. All four species are separated by marked differences in the structure of the lips of the lorica aperture and the shape of the macronucleus. Lagenophrys labiata, L. discoidea, and L. patina also are separated by differences in relative lengths and numbers of kinetosome rows that make up the penicular infraciliature. Instances of intraspecific and interspecific variation in the four species help to elucidate patterns of variation in taxonomic characteristics used in Lagenophrys. Some populations of L. patina were dimorphic, only the second such case found among species of Lagenophrys.