α,ß-trehalose, an intracellular substance in resting cyst of colpodid ciliates as a key to environmental tolerances.

α,α-trehalose is a well-known sugar that plays a key role in establishing tolerance to environmental stresses in many organisms, except unicellular eukaryotes. However, almost nothing is known about α,ß-trehalose, including their synthesis, function, and even presence in living organisms. In this study, we identified α,ß-trehalose in the resting cyst, a dormancy cell form characterized by extreme tolerance to environmental stresses, of the ciliated protist Colpoda cucullus, using high-performance liquid chromatography (HPLC), and a proton nuclear magnetic resonance (1H NMR). Gene expression analysis revealed that the expression of trehalose-6-phosphate synthase (TPS), glycosyltransferase (GT), alpha-amylase (AMY), and trehalose transporter 1 (TRET1), were up-regulated in encystment, while the expression of α-glucosidase 2 (AG2) and trehalase (TREH) was up-regulated in excystment. These results suggest that α,ß-trehalose is synthesized during encystment process, while and contributes to extreme tolerances to environmental stressors, stored carbohydrates, and energy reserve during resting cyst and/or during excystment.

Genomic insights into the cellular specialization of predation in raptorial protists.

BACKGROUND: Predation is a fundamental mechanism for organisms to acquire energy, and various species have evolved diverse tools to enhance their hunting abilities. Among protozoan predators, raptorial Haptorian ciliates are particularly fascinating as they possess offensive extrusomes known as toxicysts, which are rapidly discharged upon prey contact. However, our understanding of the genetic processes and specific toxins involved in toxicyst formation and discharge is still limited. RESULTS: In this study, we investigated the predation strategies and subcellular structures of seven Haptoria ciliate species and obtained their genome sequences using single-cell sequencing technology. Comparative genomic analysis revealed distinct gene duplications related to membrane transport proteins and hydrolytic enzymes in Haptoria, which play a crucial role in the production and discharge of toxicysts. Transcriptomic analysis further confirmed the abundant expression of genes related to membrane transporters and cellular toxins in Haptoria compared to Trichostomatia. Notably, polyketide synthases (PKS) and L-amino acid oxidases (LAAO) were identified as potentially toxin genes that underwent extensive duplication events in Haptoria. CONCLUSIONS: Our results shed light on the evolutionary and genomic adaptations of Haptorian ciliates for their predation strategies in evolution and provide insights into their toxic mechanisms.

Redescription and molecular phylogeny of the freshwater metopid, Castula strelkowi (Jankowski, 1964) from the Czech Republic and synonymization of Pileometopus with Castula.

The relationships of the mainly free living, obligately anaerobic ciliated protists belonging to order Metopida continue to be clarified and now comprise three families: Metopidae, Tropidoatractidae, and Apometopidae. The most species-rich genus of the Metopidae, Metopus has undergone considerable subdivision into new genera in recent years as more taxa are characterized by modern morphologic and molecular methods. The genus, Castula, was established to accommodate setae-bearing species previously assigned to Metopus: C. setosa and C. fusca, and one new species, C. flexibilis. Another new species, C. specialis, has been added since. Here we redescribe another species previously included in Metopus, using morphologic and molecular methods, and transfer it to Castula as C. strelkowi n. comb. (original combination Metopus strelkowi). We also reassess the monotypic genus, Pileometopus, which nests within the strongly supported Castula clade in 18S rRNA gene trees and conclude that it represents a morphologically divergent species of Castula.

Redescription and molecular characterization of Loxocephalus luridus Eberhard, 1862 based on Czech populations: Implications for order Loxocephalida Jankowski, 1980.

The phylogenetic and taxonomic affinities of lineages currently assigned to the non-monophyletic ciliate order Loxocephalida Jankowski (1980) within subclass Scuticociliatia Small (1967) remain unresolved. In the current study, we redescribe the morphology of the type species, Loxocephalus luridus Eberhard (1862) based on two Czech populations and include the first scanning and transmission electron microscopy images of the species. We provide the first 18S rRNA gene sequences for L. luridus and consider its phylogenetic position. Our results support the separation of Dexiotricha from Loxocephalus; however, the former genus is recovered as non-monophyletic. The monophyly of genus Dexiotricha and that of Loxocephalus + Dexiotricha is rejected. Loxocephalus luridus, together with Dexiotricha species, nests within a fully supported clade with Conchophthirus species, long presumed to belong to the Pleuronematida. Haptophrya is recovered as sister to this clade. The monophyly of the Astomatia Schewiakoff (1896) including Haptophrya is rejected. No clear morphologic synapomorphy is identified for the fully supported clade consisting of Haptophrya, Dexiotricha, Loxocephalus, and Conchophthirus.

Zoothamnium mariella sp. nov., a marine, colonial ciliate with an atypcial growth pattern, and its ectosymbiont Candidatus Fusimicrobium zoothamnicola gen. nov., sp. nov.

Ciliates are unicellular eukaryotes, regularly involved in symbiotic associations. Symbionts may colonize the inside of their cells as well as their surface as ectosymbionts. Here, we report on a new ciliate species, designated as Zoothamnium mariella sp. nov. (Peritrichia, Sessilida), discovered in the northern Adriatic Sea (Mediterranean Sea) in 2021. We found this ciliate species to be monospecifically associated with a new genus of ectosymbiotic bacteria, here proposed as Candidatus Fusimicrobium zoothamnicola gen. nov., sp. nov. To formally describe the new ciliate species, we investigated its morphology and sequenced its 18S rRNA gene. To demonstrate its association with a single species of bacterial ectosymbiont, we performed 16S rRNA gene sequencing, fluorescence in situ hybridization, and scanning electron microscopy. Additionally, we explored the two partners' cultivation requirements and ecology. Z. mariella sp. nov. was characterized by a colony length of up to 1 mm. A consistent number of either seven or eight long branches alternated on the stalk in close distance to each other. The colony developed three different types of zooids: microzooids ("trophic stage"), macrozooids ("telotroch stage"), and terminal zooids ("dividing stage"). Viewed from inside the cell, the microzooids' oral ciliature ran in 1 » turns in a clockwise direction around the peristomial disc before entering the infundibulum, where it performed another ¾ turn. Phylogenetic analyses assigned Z. mariella sp. nov. to clade II of the family Zoothamnidae. The ectosymbiont formed a monophyletic clade within the Gammaproteobacteria along with two other ectosymbionts of peritrichous ciliates and a free-living vent bacterium. It colonized the entire surface of its ciliate host, except for the most basal stalk of large colonies, and exhibited a single, spindle-shaped morphotype. Furthermore, the two partners together appear to be generalists of temperate, oxic, marine shallow-water environments and were collectively cultivable in steady flow-through systems.

Using digital PCR to predict ciliate abundance from ribosomal RNA gene copy numbers.

Ciliates play a key role in most ecosystems. Their abundance in natural samples is crucial for answering many ecological questions. Traditional methods of quantifying individual species, which rely on microscopy, are often labour-intensive, time-consuming and can be highly biassed. As a result, we investigated the potential of digital polymerase chain reaction (dPCR) for quantifying ciliates. A significant challenge in this process is the high variation in the copy number of the taxonomic marker gene (ribosomal RNA [rRNA]). We first quantified the rRNA gene copy numbers (GCN) of the model ciliate, Paramecium tetraurelia, during different stages of the cell cycle and growth phases. The per-cell rRNA GCN varied between approximately 11,000 and 130,000, averaging around 50,000 copies per cell. Despite these variations in per-cell rRNA GCN, we found a highly significant correlation between GCN and cell numbers. This is likely due to the coexistence of different cellular stages in an uncontrolled (environmental) ciliate population. Thanks to the high sensitivity of dPCR, we were able to detect the target gene in a sample that contained only a single cell. The dPCR approach presented here is a valuable addition to the molecular toolbox in protistan ecology. It may guide future studies in quantifying and monitoring the abundance of targeted (even rare) ciliates in natural samples.

High infestation and phylogenetic position of Epistylis sp. (Ciliophora, Peritrichia) on Aegla serrana Buckup & Rossi (Crustacea, Anomura) from southern Brazil.

High infestations of epibiont ciliates on vertebrates or invertebrates are normally related to aquaculture tanks or similar environments, and the importance of this relationship in natural habitats is often disregarded. Here, we describe the first record of high infestation of ciliates on Aegla serrana in South America and conduct a brief morphological and phylogenetic characterization of these ciliates. Our findings confirm that cases of high infestation of ciliates on metazoans can indeed occur in natural environments.

Coinfection of slime feather duster worms (Annelida, Myxicola) by different gregarine apicomplexans (Selenidium) and astome ciliates reflects spatial niche partitioning and host specificity.

Individual organisms can host multiple species of parasites (or symbionts), and one species of parasite can infect different host species, creating complex interactions among multiple hosts and parasites. When multiple parasite species coexist in a host, they may compete or use strategies, such as spatial niche partitioning, to reduce competition. Here, we present a host­symbiont system with two species of Selenidium (Apicomplexa, Gregarinida) and one species of astome ciliate co-infecting two different species of slime feather duster worms (Annelida, Sabellidae, Myxicola) living in neighbouring habitats. We examined the morphology of the endosymbionts with light and scanning electron microscopy (SEM) and inferred their phylogenetic interrelationships using small subunit (SSU) rDNA sequences. In the host 'Myxicola sp. Quadra', we found two distinct species of Selenidium; S. cf. mesnili exclusively inhabited the foregut, and S. elongatum n. sp. inhabited the mid to hindgut, reflecting spatial niche partitioning. Selenidium elongatum n. sp. was also present in the host M. aesthetica, which harboured the astome ciliate Pennarella elegantia n. gen. et sp. Selenidium cf. mesnili and P. elegantia n. gen. et sp. were absent in the other host species, indicating host specificity. This system offers an intriguing opportunity to explore diverse aspects of host­endosymbiont interactions and competition among endosymbionts.

Decryption of the survival "black box": gene family expansion promotes the encystment in ciliated protists.

BACKGROUND: Encystment is an important survival strategy extensively employed by microbial organisms to survive unfavorable conditions. Single-celled ciliated protists (ciliates) are popular model eukaryotes for studying encystment, whereby these cells degenerate their ciliary structures and develop cyst walls, then reverse the process under more favorable conditions. However, to date, the evolutionary basis and mechanism for encystment in ciliates is largely unknown. With the rapid development of high-throughput sequencing technologies, genome sequencing and comparative genomics of ciliates have become effective methods to provide insights into above questions. RESULTS: Here, we profiled the MAC genome of Pseudourostyla cristata, a model hypotrich ciliate for encystment studies. Like other hypotrich MAC genomes, the P. cristata MAC genome is extremely fragmented with a single gene on most chromosomes, and encodes introns that are generally small and lack a conserved branch point for pre-mRNA splicing. Gene family expansion analyses indicate that multiple gene families involved in the encystment are expanded during the evolution of P. cristata. Furthermore, genomic comparisons with other five representative hypotrichs indicate that gene families of phosphorelay sensor kinase, which play a role in the two-component signal transduction system that is related to encystment, show significant expansion among all six hypotrichs. Additionally, cyst wall-related chitin synthase genes have experienced structural changes that increase them from single-exon to multi-exon genes during evolution. These genomic features potentially promote the encystment in hypotrichs and enhance their ability to survive in adverse environments during evolution. CONCLUSIONS: We systematically investigated the genomic structure of hypotrichs and key evolutionary phenomenon, gene family expansion, for encystment promotion in ciliates. In summary, our results provided insights into the evolutionary mechanism of encystment in ciliates.

Redescription and molecular phylogeny of Trochilia sigmoides Dujardin, 1841 (Ciliophora, Cyrtophoria) collected from South Korea.

During a survey of Korean marine ciliates, Trochilia sigmoides, the type species of the genus Trochilia, was collected and examined using in vivo observation and protargol impregnation. Moreover, scanning electron microscopy and 18S rRNA gene sequencing have been applied for the first time to study this species. Morphologically, T. sigmoides is characterized by the small body size, the oval body outline, and the spiral dorsal ridges. The Korean population of T. sigmoides shows only minute differences to other populations reported in the literature, mainly in body size and the number of dorsal ridges. Phylogenetic analyses based on 18S rRNA gene sequences show that T. sigmoides and T. petrani are placed together with two members of the family Kyaroikeidae, causing the family Dysteriidae to be non-monophyletic. The present new data increase the knowledge about the morphology and phylogeny of the genus Trochilia and would assist in understanding the phylogenetic relationship between the free-living Dysteriidae and the parasitic Kyaroikeidae.

Single-cell transcriptomic analysis reveals genome evolution in predatory litostomatean ciliates.

Many ciliated protists prey on other large microbial organisms, including other protists and microscopic metazoans. The ciliate class Litostomatea unites both predatory and endosymbiotic species. The evolution of predation ability in ciliates remains poorly understood, in part, due to a lack of genomic data. To fill this gap, we acquired the transcriptome profiles of six predatory litostomateans using single-cell sequencing technology and investigated their transcriptomic features. Our results show that: (1) in contrast to non-predatory ciliates, the predatory litostomateans have expanded gene families associated with transmembrane activity and reactive oxidative stress response pathways, potentially as a result of cellular behaviors such as fast contraction and extension; (2) the expansion of the calcium-activated BK potassium channel gene family, which hypothetically regulates cell contractility, is an ancient evolutionary event for the class Litostomatea, suggesting a rewired metabolism associated with the hunting behavior of predatory ciliates; and (3) three whole genome duplication (WGD) events have been detected in litostomateans, with genes associated with biosynthetic processes, transmembrane activity, and calcium-activated potassium channel activity being retained during the WGD events. In addition, we explored the evolutionary relationships among 17 ciliate species, including eight litostomateans, and provided a rich foundational dataset for future in-depth phylogenomic studies of Litostomatea. Our comprehensive analyses suggest that the rewired cellular metabolism via expanded gene families and WGD events might be the potential genetic basis for the predation ability of raptorial ciliates.

Flatworm Transcriptomes Reveal Widespread Parasitism by Histophagous Ciliates.

Unicellular ciliates like Tetrahymena are best known as free-living bacteriovores, but many species are facultative or obligate parasites. These "histophages" feed on the tissues of hosts ranging from planarian flatworms to commercially important fish and the larvae of imperiled freshwater mussels. Here, we developed a novel bioinformatics pipeline incorporating the nonstandard ciliate genetic code and used it to search for Ciliophora sequences in 34 publicly available Platyhelminthes EST libraries. From 2,615,036 screened ESTs, we identified nearly 6,000 high-confidence ciliate transcripts, supporting parasitism of seven additional flatworm species. We also cultured and identified Tetrahymena from nine terrestrial and freshwater planarians, including invasive earthworm predators from the genus Bipalium and the widely studied regeneration models Dugesia japonica and Schmidtea mediterranea. A co-phylogenetic reconstruction provides strong evidence for the coevolution of histophagous Ciliophora with their Platyhelminthes hosts. We further report the antiprotozoal aminoglycoside paromomycin expels Tetrahymena from S. mediterranea, providing new opportunities to investigate the effects of this relationship on planarian biology. Together, our findings raise the possibility that invasive flatworms constitute a novel dispersal mechanism for Tetrahymena parasites and position the Platyhelminthes as an ideal model phylum for studying the ecology and evolution of histophagous ciliates.

Systematic review of the genera Rhabdostyla Kent 1880 and Orborhabdostyla Foissner et al. 2010 (Ciliophora, Peritrichia, Epistylididae).

The genus Rhabdostyla is one of the oldest of the family Epistylididae, it was described over 120 years ago and has more than 40 species considered valid. This group went through several systematic changes throughout its existence and due to the lack of taxonomic information, said to be essential, for most species that compose it, some of these changes are still questioned. In order to better understand and validate the species and relationships identified for this genus, the present work makes a brief review for the genus Rhabdostyla and its related genera, Opisthostyla and Orborhabdostyla. A 18S-rDNA phylogenetic analysis was also performed to understand the relationship between these groups. As a result of this review, 45 diagnoses were compiled and reorganized for the current model, accompanied by new graphical representations for the species considered valid for the genus Rhabdostyla and its associates. The major changes that the genus underwent, such as synonymy and separation to a new genus, were discussed in light of new phylogenetic information, but despite this, other information is still needed for a better validation of these changes.

Mitogenomic architecture and evolution of the soil ciliates Colpoda.

Colpoda are cosmopolitan unicellular eukaryotes primarily inhabiting soil and benefiting plant growth, but they remain one of the least understood taxa in genetics and genomics within the realm of ciliated protozoa. Here, we investigate the architecture of de novo assembled mitogenomes of six Colpoda species, using long-read sequencing and involving 36 newly isolated natural strains in total. The mitogenome sizes span from 43 to 63 kbp and typically contain 28-33 protein-coding genes. They possess a linear structure with variable telomeres and central repeats, with one Colpoda elliotti strain isolated from Tibet harboring the longest telomeres among all studied ciliates. Phylogenomic analyses reveal that Colpoda species started to diverge more than 326 million years ago, eventually evolving into two distinct groups. Collinearity analyses also reveal significant genomic divergences and a lack of long collinear blocks. One of the most notable features is the exceptionally high level of gene rearrangements between mitochondrial genomes of different Colpoda species, dominated by gene loss events. Population-level mitogenomic analysis on natural strains also demonstrates high sequence divergence, regardless of geographic distance, but the gene order remains highly conserved within species, offering a new species identification criterion for Colpoda species. Furthermore, we identified underlying heteroplasmic sites in the majority of strains of three Colpoda species, albeit without a discernible recombination signal to account for this heteroplasmy. This comprehensive study systematically unveils the mitogenomic structure and evolution of these ancient and ecologically significant Colpoda ciliates, thus laying the groundwork for a deeper understanding of the evolution of unicellular eukaryotes.IMPORTANCEColpoda, one of the most widespread ciliated protozoa in soil, are poorly understood in regard to their genetics and evolution. Our research revealed extreme mitochondrial gene rearrangements dominated by gene loss events, potentially leading to the streamlining of Colpoda mitogenomes. Surprisingly, while interspecific rearrangements abound, our population-level mitogenomic study revealed a conserved gene order within species, offering a potential new identification criterion. Phylogenomic analysis traced their lineage over 326 million years, revealing two distinct groups. Substantial genomic divergence might be associated with the lack of extended collinear blocks and relaxed purifying selection. This study systematically reveals Colpoda ciliate mitogenome structures and evolution, providing insights into the survival and evolution of these vital soil microorganisms.

Somatic genome architecture and molecular evolution are decoupled in "young" linage-specific gene families in ciliates.

The evolution of lineage-specific gene families remains poorly studied across the eukaryotic tree of life, with most analyses focusing on the recent evolution of de novo genes in model species. Here we explore the origins of lineage-specific genes in ciliates, a ~1 billion year old clade of microeukaryotes that are defined by their division of somatic and germline functions into distinct nuclei. Previous analyses on conserved gene families have shown the effect of ciliates' unusual genome architecture on gene family evolution: extensive genome processing-the generation of thousands of gene-sized somatic chromosomes from canonical germline chromosomes-is associated with larger and more diverse gene families. To further study the relationship between ciliate genome architecture and gene family evolution, we analyzed lineage specific gene families from a set of 46 transcriptomes and 12 genomes representing x species from eight ciliate classes. We assess how the evolution lineage-specific gene families occurs among four groups of ciliates: extensive fragmenters with gene-size somatic chromosomes, non-extensive fragmenters with "large'' multi-gene somatic chromosomes, Heterotrichea with highly polyploid somatic genomes and Karyorelictea with 'paradiploid' somatic genomes. Our analyses demonstrate that: 1) most lineage-specific gene families are found at shallow taxonomic scales; 2) extensive genome processing (i.e., gene unscrambling) during development likely influences the size and number of young lineage-specific gene families; and 3) the influence of somatic genome architecture on molecular evolution is increasingly apparent in older gene families. Altogether, these data highlight the influences of genome architecture on the evolution of lineage-specific gene families in eukaryotes.

Single cell transcriptomics reveals UAR codon reassignment in Palmarella salina (Metopida, Armophorea) and confirms Armophorida belongs to APM clade.

Anaerobes have emerged in several major lineages of ciliates, but the number of independent transitions to anaerobiosis among ciliates is unknown. The APM clade (Armophorea, Muranotrichea, Parablepharismea) represents the largest clade of obligate anaerobes among ciliates and contains free-living marine and freshwater representatives as well as gut endobionts of animals. The evolution of APM group has only recently started getting attention, and our knowledge on its phylogeny and genetics is still limited to a fraction of taxa. While ciliates portray a wide array of alternatives to the standard genetic code across numerous classes, the APM ciliates were considered to be the largest group using exclusively standard nuclear genetic code. In this study, we present a pan-ciliate phylogenomic analysis with emphasis on the APM clade, bringing the first phylogenomic analysis of the family Tropidoatractidae (Armophorea) and confirming the position of Armophorida within Armophorea. We include five newly sequenced single cell transcriptomes from marine, freshwater, and endobiotic APM ciliates - Palmarella salina, Anteclevelandella constricta, Nyctotherus sp., Caenomorpha medusula, and Thigmothrix strigosa. We report the first discovery of an alternative nuclear genetic code among APM ciliates, used by Palmarella salina (Tropidoatractidae, Armophorea), but not by its close relative, Tropidoatractus sp., and provide a comparative analysis of stop codon identity and frequency indicating the precedency to the UAG codon loss/reassignment over the UAA codon reassignment in the specific ancestor of Palmarella. Comparative genomic and proteomic studies of this group may help explain the constraints that underlie UAR stop-to-sense reassignment, the most frequent type of alternative nuclear genetic code, not only in ciliates, but eukaryotes in general.

Deciphering phylogenetic relationships of and delimiting species boundaries within the controversial ciliate genus Conchophthirus using an integrative morpho-evo approach.

The phylum Ciliophora (ciliates) comprises about 2600 symbiotic and over 5500 free-living species. The inclusion of symbiotic ciliates in phylogenetic analyses often challenges traditional classification frameworks due to their morphological adaptions to the symbiotic lifestyle. Conchophthirus is such a controversial obligate endocommensal genus whose affinities to other symbiotic and free-living scuticociliates are still poorly understood. Using uni- and multivariate morphometrics as well as 2D-based molecular and phylogenetic analyses, we attempted to test for the monophyly of Conchophthirus, study the boundaries of Conchophthirus species isolated from various bivalves at mesoscale, and reveal the phylogenetic relationships of Conchophthirus to other scuticociliates. Multidimensional analyses of morphometric and cell geometric data generated the same homogenous clusters, as did phylogenetic analyses based on 144 new sequences of two mitochondrial and five nuclear molecular markers. Conchophthirus is not closely related to 'core' scuticociliates represented by the orders Pleuronematida and Philasterida, as assumed in the past using morphological data. Nuclear and mitochondrial markers consistently showed the free-living Dexiotricha and the mouthless endosymbiotic Haptophrya to be the nearest relatives of Conchophthirus. These three highly morphologically and ecologically dissimilar genera represent an orphan clade from the early radiation of scuticociliates in molecular phylogenies.

Morphogenesis of an anaerobic ciliate Heterometopus palaeformis (Kahl, 1927) Foissner, 2016 (Ciliophora, Armophorea) with notes on its morphological and molecular characterization.

The morphology, morphogenesis, and molecular phylogeny of Heterometopus palaeformis (Kahl, 1927) Foissner, 2016 were studied using microscopical observations on live and protargol-stained specimens as well SSU rRNA gene sequencing. The morphogenetic data for the genus are presented for the first time. Compared to other metopids, the morphogenesis of H. palaeformis is distinct since its (1) perizonal stripe rows 4 and 5 are involved in the formation of the opisthe's adoral polykinetids; (2) perizonal stripe rows 3-5 and two adjacent preoral dome kineties contribute to most of the opisthe's paroral membrane while perizonal stripe rows 1 and 2 contribute very little; (3) four kinety rows are formed to the left of the opisthe's adoral zone of polykinetids. The Chinese population resembles the original and neotype populations well in terms of general morphology - characterized by a life size of 55-120 × 10-20 µm, an elongate ellipsoidal body with a hardly spiralized flat preoral dome, about 18 somatic kineties and 20 adoral polykinetids. The SSU rDNA sequence of the present population exhibits a disparity of 1.33%-2.22% divergence from sequences of other populations. Nevertheless, phylogenetic analysis reveals that populations of H. palaeformis form a separate, stable cluster within the paraphyletic Metopidae clade.

Morphology and molecular phylogeny of two hypotrichous ciliates (Ciliophora, Spirotrichea) from South Korea, including Hemiurosomoida koreana n. sp.

The living morphology, infraciliature, and molecular phylogeny of a new soil ciliate, Hemiurosomoida koreana n. sp., discovered in a sample collected from a mountain in the northeast of South Korea, were investigated. The new species possesses the characteristics of the genus Hemiurosomoida, i.e., a reduced number of frontal-ventral-transverse cirri, three dorsal kineties of which kineties 1 and 2 each bears a caudal cirrus, and a single dorsomarginal kinety. It is distinguishable from congeners and other similar species by at least one distinct qualitative or quantitative character including the body size, the presence and arrangement of cortical granules, the number of adoral membranelles, marginal cirri, and dorsal dikinetids, or by the arrangement of transverse cirri. Phylogenetic analyses based on 18S rRNA gene sequences also support the assignment of the new species to the non-monophyletic genus Hemiurosomoida. In addition, the living morphology, infraciliature, and the 18S rRNA gene sequence of a Korean population of Nothoholosticha flava were studied.

Morphology, morphogenesis, and molecular phylogeny of Aspidisca koreana n. sp. (Ciliophora, Euplotida) from South Korea.

The morphology, morphogenesis, and molecular phylogeny of a new ciliate, Aspidisca koreana n. sp., discovered in the eastern coast of South Korea, were investigated. The morphological description is based on the observation of living cells, 4'-6-diamidino-2-phenylindole (DAPI) and silver-stained specimens (e.g., protargol, silver nitrate), and scanning electron micrographs. The new species is characterized by having a small body size (17-25 × 15-18 µm in vivo), a distinct peristomial spur on the posterior portion of left margin, seven frontoventral cirri in "polystyla-arrangement", and the arrangement of the anterior portion of adoral zone of membranelles, i.e., anteriormost membranelle is distinctly separated from the other three membranelles. The morphogenesis follows the typical pattern of this genus. Phylogenetic analyses, using the 18S rDNA sequence, also support the establishment of a new species.