Morphology, Morphogenesis, and Molecular Phylogeny of Neobakuella aenigmatica n. sp. (Ciliophora, Spirotrichea, Bakuellidae)

Polymorphism, gigantism, and cannibalism, one stylonychid ciliate (Ciliophora, Hypotricha) to rule them all

The morphology, ontogenesis, and molecular phylogeny of the polymorphic and cannibalistic giant forming Tetmemena polymorpha n. sp., found in a brackish water sample in South Korea, were investigated. The present species has long been misidentified as "Oxytricha bifaria." The new investigation shows that the species produces three morphologically different morphs. The small morph is bacterivorous and characterized by its small body size and slim body and it is found only in the stationary and decline phases of the culture. The large morph has a wide body, larger oral apparatus, and feeds on small eukaryotes such as yeast cells and small ciliates. It divides very quickly and produces the other two morphs and found in the exponential phase of the cultures. The giant morph is characterized by its huge body and oral apparatus. It feeds on the small morph cells of the same species and other ciliates, and occurs together with the small morph. Phylogenetic analyses based on the 18S rRNA gene sequences show that the new species is placed in a sister subclade to that containing other Tetmemena sequences. Moreover, Tetmemena indica Bharti et al., 2019 nov. stat. is raised to species level based on the differences in the cyst morphology and the dorsal ciliature to the authoritative Tetmemena pustulata population.

Morphology and Molecular Phylogeny of Two New Trachelophyllid Ciliates, Monolamellophrya terricola gen. nov., sp. nov. and Trachelophyllum parapiculatum sp. nov. (Litostomatea, Haptoria), From South Korea

The morphology and molecular phylogeny of two new ciliates, Monolamellophrya terricola gen. nov., sp. nov. and Trachelophyllum parapiculatum sp. nov., discovered in South Korea, were investigated. The two species belong to the suborder Trachelophyllina, which is characterized by the presence of a mucilaginous layer containing lepidosomes covering the cortex. Monolamellophrya terricola gen. nov., sp. nov. is characterized by the presence of a single layer of type II lepidosomes, representing a new genus. Trachelophyllum parapiculatum sp. nov. has only type I lepidosomes covering the cortex, a generic character of the genus Trachelophyllum, and is distinguished from other congeners by a combination of morphological features, including the 15–24 μm long rod-shaped extrusomes, the 9–13 ciliary rows, the 7–11 and 17–25 dikinetids in brush rows 1 and 2, respectively, and the bipolar brush row 3. Furthermore, the 18S rRNA gene sequences of the two new species were provided. The phylogenetic analyses show that the sequence of M. terricola gen. nov., sp. nov. clusters with two other trachelophyllid sequences, and the sequence of T. parapiculatum sp. nov. is placed at the base of these three sequences with full support. Furthermore, the four trachelophyllid sequences that are available so far form a monophyletic clade.

Redescription of Bakuella (Bakuella) marina Agamaliev and Alekperov, 1976 (Protozoa, Hypotrichia), With Notes on Its Morphology, Morphogenesis, and Molecular Phylogeny

Because the original description of Bakuella (Bakuella) marina, type of the genus, is only based on protargol-impregnated specimens, one of the important living features, namely, the presence/absence of cortical granules, remains unknown so far. In the present work, a detailed investigation of a Chinese population of B. (Bakuella) marina is carried out using the integrated approaches, and the live morphology, ontogenesis, and molecular information of B. (Bakuella) marina are presented for the first time. The infraciliature of this population corresponds perfectly with that of the original description. The in vivo observation indicates that B. (Bakuella) marina possesses colorless cortical granules. The most prominent morphogenetic feature of B. (Bakuella) marina is that the parental adoral zone of membranelles is completely replaced by the newly formed one of the proters. Molecular phylogenetic analysis based on a small subunit ribosomal gene (SSU rDNA) shows that five Bakuella species are clustered with the species from other six Urostylid genera, namely, Anteholosticha, Apobakuella, Diaxonella, Holosticha, Neobakuella, and Urostyla. The monophyletic probabilities of the family Bakuellidae, genus Bakuella, subgenus B. (Bakuella), and subgenus B. (Pseudobakuella) are rejected by the approximately unbiased test. This study further shows that the family Bakuellidae, genus Bakuella, and subgenus B. (Bakuella) are all nonmonophyletic groups. In order to establish a reasonable classification system, information on molecular and morphogenesis of more Bakuellids and its related species is urgently needed.

New Contributions to the Diversity of Hypotrichous Ciliates: Description of a New Genus and Two New Species (Protozoa, Ciliophora)

Ciliated protists (ciliates) are extremely diverse and play important ecological roles in almost all kinds of habitats. In this study, two new hypotrichs, Wilbertophrya sinica n. g. and n. sp. and Bakuella xianensis n. sp., from China are investigated. Wilbertophrya n. g. can be separated from related genera mainly by the combination of lacking a buccal cirrus, pretransverse cirri, and caudal cirri, while possessing frontoterminal cirri. Analyses based on morphological and molecular data confirm the validity of the species, W. sinica n. sp., which is characterized as follows: body 50-115 μm × 15-35 μm in vivo; midventral complex comprises four or five cirral pairs only and terminates above mid-body; three frontal, two frontoterminal cirri, and two to four transverse cirri; about 15 macronuclear nodules; colorless cortical granules sparsely distributed. Another new species, B. xianensis n. sp., was isolated from a freshwater wetland and is defined as follows: body 115-150 μm × 40-65 μm in vivo; about 70 macronuclear nodules; dark-brownish cortical granules in groups; midventral complex comprises 8-12 cirral pairs forming a row that terminates posteriorly in mid-body region and two or three short midventral rows that are continuous with the row of midventral pairs; three frontal, four to six frontoterminal, and three to five fine transverse cirri; three bipolar dorsal kineties. Phylogenetic analyses based on small subunit ribosomal DNA (SSU rDNA) sequence data suggest that the new genus Wilbertophrya n. g. belongs to an isolated clade, which might represent an undescribed taxon at the family level, whereas B. xianensis n. sp. groups with several congeners and members of other related genera are within the core urostylids.

Taxonomy and Molecular Phylogeny of Two New Urostylid Ciliates (Protozoa: Ciliophora) From Chinese Wetlands and Establishment of a New Genus

Hypotrich ciliates with evolutionary novelties are continually being discovered, challenging the current taxonomic system and attracting increased attention. In the present work, two new urostylid ciliates, Heterobakuella bergeri gen. nov., sp. nov. and Anteholosticha perezuzae sp. nov., isolated from Chinese wetland samples, were identified based on morphology and 18S rRNA gene sequences. Heterobakuella gen. nov. is defined by three frontal cirri, single buccal cirrus, one parabuccal cirrus, midventral complex composed of cirral pairs and one cirral row, one left and two right marginal cirral rows, transverse and pretransverse cirri present, caudal and frontoterminal cirri absent. Heterobakuella can be easily distinguished from the morphologically most similar genus, Apobakuella, mainly by the single buccal cirrus (vs. one buccal cirral row) and one parabuccal cirrus (vs. several parabuccal cirral rows originated from different anlagen). Phylogenetic analyses show that H. bergeri branches within the clade formed by Bergeriella ovata, Monocoronella carnea, Anteholosticha gracilis, and Neourostylopsis spp., rather than the clade represented by Apobakuella. The other species, A. perezuzae, is mainly characterized by a distinctly slender body shape with an average length:width ratio about 7, distinctively shaped biconcave and greenish cortical granules, as well as one or two pretransverse cirri. Phylogenetic analyses indicate the genus Anteholosticha is non-monophyletic.

Tunicothrix halophila n. sp., a Secondarily Oligomerized Parabirojimid Hypotrich (Ciliophora, Spirotrichea) From Hypersaline Costal Water in Korea

Tunicothrix halophila n. sp. was discovered in a hypersaline marine sample from Jeju Island, Korea. It is characterized by the highly reduced number of dorsal bristles. In addition, the main character of the genus Tunicothrix (e.g., alveolar layer) is absent/indistinct. To figure out its identity and phylogenetic relationship, we examined the new species based on modern morphological methods and molecular phylogenetic analyses. Since the parabirojimids are of basal position to core hypotrichs and a smaller data set could show incorrect phylogenetic relationships among the hypotrichs, we used a huge data set composed of 1,460 DNA sequences to infer the phylogenetic tree. The reduction of dorsal bristles is very likely a secondarily evolved character in hypotrichs, resulting in the independent phenotypic adaptation in the hypersaline ecosystems as shown in other hypersaline hypotrichs. Furthermore, the so-called right marginal row 1 in other congeners is found to produce a pretransverse and transverse cirrus and thus we recommend using the term frontoventral row. Based on our data, we can justify Tunicothrix halophila n. sp. as a new species; however, despite the phenotypic distinctiveness, we refrain to establish a new genus because of the missing data and the non-monophyly of Tunicothrix.

New contributions to the taxonomy of urostylid ciliates (Ciliophora, Hypotrichia), with establishment of a new genus and new species

Hypotrichia, one of the most complex and highly differentiated groups in Ciliophora, has been the object of extensive studies, especially in recent years. Nevertheless, methodological difficulties and insufficient faunistic studies have limited our understanding of their biodiversity and phylogeny. In this study, one novel urostylid ciliate, Pseudoholosticha zhaoi nov. gen., nov. spec. and two populations of Anteholosticha monilata (Kahl, 1928) Berger, 2003, type species of the latter genus, are studied using an integrative approach (live observation, protargol impregnation, scanning electron microscopy, and phylogenetic analysis) to provide further insights into the diversity, classification, and phylogeny of this group of ciliates. Pseudoholosticha nov. gen. can be separated from other morphologically similar genera mainly by the absence of buccal and caudal cirri. A key to 12 morphologically similar genera and illustrations of their cirral patterns are provided. The validation of the new genus and new species is supported by both morphological and phylogenetic analyses. The first 18S rRNA gene sequence of A. monilata, with detailed morphological data, provided a reliable clarification of A. monilata populations and corroborated the phylogenetic position of the type species of the polyphyletic genus Anteholosticha.

Molecular phylogeny of a new gonostomatid ciliate revealing a discrepancy between interphasic and cell divisional patterns (Ciliophora, Hypotricha)

The morphology, ontogenesis, and molecular phylogeny of a new ciliate, Gonostomum koreanum n. sp., discovered in a terrestrial moss sample from South Korea, were investigated. Morphologically, it is characterized by a gonostomatid oral apparatus, two macronuclear nodules, six frontoventral rows, the two rightmost of which (frontoventral rows V and VI) extend posteriorly to near pretransverse and transverse cirri, and three dorsal kineties each with a single caudal cirrus posteriorly. The new species is easily confused with members of the genus Metagonostomum because of the long frontoterminal cirral row but differs mainly in the de novo (vs. intrakinetal) origin of anlage VI, a character found only in Gonostomum and Paragonostomum. To solve the discrepancy between the interphasic and ontogenetic patterns, we additionally performed morphological and multigene analyses on three gonostomatid species, namely Gonostomum koreanum n. sp. and its morphologically (M. gonostomoida) and ontogenetically (G. kuehnelti) most similar species. The multigene analyses show that the new species is closely related to G. kuehnelti and the core gonostomatids consists of five groups based on the origin of the frontoventral rows.

Some morphologically distinguishable hypotrich ciliates share identical 18S rRNA gene sequences – taxonomic insights from a case study on Oxytricha species (Protista, Ciliophora)

Modern taxonomic studies of ciliated protozoa require both morphological and molecular data. One dilemma is how to distinguish morphologically similar species with few nucleotide differences in the widely used marker, the 18S rRNA gene. In the present study, two Oxytricha species were morphologically documented using light and electron microscopy. The mitochondrial cytochrome c oxidase subunit I (COI) gene and a fragment of the rRNA gene covering the 18S-ITS1-5.8S-ITS2-28S rRNA gene regions were sequenced. Phylogenetic analyses of all available Oxytricha granulifera-related populations were performed to reveal the internal relationships of this group. We described a new species, Oxytricha atypica sp. nov., distinguished from its congeners by having seven postoral ventral cirri resulting from the additional fragmentation of anlage V during ontogenesis. Although their 18S rRNA genes differ by only one nucleotide, divergence of the COI gene is as high as 11.8% between O. atypica and the closely related species, O. granulifera. All but one of the COI nucleotide substitutions were synonymous. We documented the highly conserved nature of the 18S rRNA gene in the morphospecies of Oxytricha. Based on these findings, we speculate that O. granulifera contains cryptic species or morphospecies needing further characterization, and new insights for the taxonomy of hypotrich ciliates are also discussed.

Description and Morphogenesis of a Chinese Population of Bakuella granulifera Foissner, Agatha and Berger, 2002 (Ciliophora, Hypotricha)

In this study, the morphology and morphogenesis of Bakuella granulifera Foissner, Agatha, and Berger, 2002, isolated from soil in the Chanba National Wetland Park, Xi'an, China, were studied based on in vivo observations and protargol staining. The Chinese population is distinctly smaller than the type population from Namibia. Details of the ontogenetic process are provided for the first time and are summarized as follows: (1) the parental adoral zone is partly retained; (2) the left of the endoral forms a rather wide anlage and the proximal adoral membranelles are renewed; (3) the parental midventral complex contributes to the formation of the FVT cirral anlagen; (4) the marginal rows anlagen and dorsal kineties anlagen develop intrakinetally; (5) no caudal cirri are produced; and (6) the macronuclear nodules fuse to a single mass. In combination with previous studies, these findings suggest that the genus Bakuella is ontogenetically diverse.

Morphology and morphogenesis of a Chinese population of a soil urostylid ciliate, Extraholosticha sylvatica (Foissner, 1982) Li et al., 2017 (Ciliophora, Hypotrichia)

A soil urostylid ciliate Extraholosticha sylvatica, isolated from southern China, is studied using live observation and protargol impregnation. The main ontogenetic features of E. sylvatica are as follows: (a) in the proter, only the posterior part of the parental adoral zone of membranelles is renewed, while the anterior portion is retained; undulating membranes anlage undergo, like most hypotrichs, depolymerization of old undulating membranes and differentiation of new structures; (b) the oral primordium in the opisthe and the frontoventraltransverse cirral anlagen in both daughter cells are formed with contribution of the parental midventral cirri; (c) three frontal, one buccal, three to five frontoventral, one or two frontoterminal, two or three pretransverse ventral and six to 11 transverse cirri and 16–22 midventral pairs are generated from frontoventral-transverse cirral anlagen; (d) in both the left and the right marginal rows as well as the dorsal kineties, each two anlagen are formed intrakinetally; three to six caudal cirri are formed at the posterior end of the 5th dorsal kinety anlage; (e) the macronuclear nodules fuse into a single mass during the process.