Marginal Rows Research Articles

Morphology, ontogeny, and molecular phylogeny of two novel bakuellid-like hypotrichs (Ciliophora: Hypotrichia), with establishment of two new genera

The morphology, ontogeny and molecular phylogeny of Apobakuella fusca gen. n., sp. n. and Parabistichella variabilis gen. n., sp. n., from south China were investigated. Apobakuella fusca, brown colored, demonstrates bakuellid-like infraciliature, and a similar ontogenesis as the genus Bakuella. It is argued, however, that this species represents a novel genus, Apobakuella, which is characterized by two or more marginal rows on the right, several buccal and parabuccal cirri, and lack of frontoterminal and caudal cirri. Phylogenetic analysis based on SSU rRNA gene sequences supports the close relationship of Apobakuella with Neobakuella and Diaxonella within the core Urostylida. By contrast, Parabistichella variabilis has a dominant frontoventral row, few midventral pairs, a long midventral row, and one marginal row on each side. Its morphogenesis exhibits: (1) partial reorganization of the parental adoral membranelles; (2) over six frontoventral-transverse cirri anlagen; (3) intrakinetal development of the midventral row; and (4) very likely, formation of the frontoventral row from the midventral row anlage. Both the morphological characteristics and the SSU rRNA gene sequences suggest that it is incertae sedis among the basal hypotrichs. Further investigation of key taxa with additional molecular markers is required to reveal a better understanding on the phylogeny of Parabistichella.

Establishment of a new hypotrichous genus, Heterotachysoma n. gen. and notes on the morphogenesis of Hemigastrostyla enigmatica (Ciliophora, Hypotrichia)

A marine hypotrich ciliate, Heterotachysoma multinucleatum (Gong and Choi, 2007) n. comb., found in coastal waters near Qingdao, China, was investigated. Heterotachysoma multinucleatum is characterized by its dorsal ciliature arranged in Gonostomum-pattern. Additionally, a new genus, Heterotachysoma n. gen., is established which is mainly characterized by: 18-cirri pattern; flexible body; three dorsal kineties with no dorsomarginal kineties nor kinety fragmentation; one right and one left row of marginal cirri; caudal cirri absent. The genus Tachysoma is redefined, and three new combinations, T. multinucleatum, T. ovatum and T. dragescoi, are proposed. The morphogenesis of Hemigastrostyla enigmatica (Dragesco and Dragesco-Kernéis, 1986) Song and Wilbert, 1997, is also described. Compared with that of its congeners, the differences are mainly in the dorsal ciliature: (1) the dorsal kinety anlagen are formed de novo in H. enigmatica (vs. intrakinetally in H. paraenigmatica and H. elongata); (2) the dorsal kineties anlagen develop in secondary mode in H. enigmatica (vs. primary mode in H. paraenigmatica); (3) the kinetal fragment anterior to the right marginal row in both filial product is absent in both H. enigmatica and H. elongata (vs. present in H. paraenigmatica). These findings suggest that morphogenesis is not uniform among members of the genus Hemigastrostyla.

Redescription of Two Urostylid Ciliates (Ciliophora: Urostylida), Anteholosticha pulchra and Metaurostylopsis struederkypkeae from Korea

Two urostylid ciliates, Anteholosticha pulchra (Kahl, 1932) Berger, 2003 and Metaurostylopsis struederkypkeae Shao et al., 2008, new to Korea, were collected from the Yellow Sea and the East Sea, Korea, respectively. They were identified based on live observation and protargol impregnation. Taxonomical characters of A. pulchra are as follows: <TEX>$190-300{\times}30-55\;{\mu}m$</TEX> size in vivo; contractile vacuole located on the left side of the posterior 1/4 of the cell; spherical-reddish granules at cirral bases and around dorsal bristles, somewhat sparsely distributed throughout the cell surface; four frontal and two frontoterminal cirri; four dorsal kineties; caudal cirri absent. Metaurostylopsis struederkypkeae is characterized as follows: <TEX>$80-110{\times}40-50\;{\mu}m$</TEX> size in vivo; caudal cirri absent; two types of cortical granules: type 1, yellow-green arranged along the ventral cirral rows and dorsal kineties; type 2, small and reddish, with an irregular arrangement; four frontal, four to eight frontoterminal, and two to six transverse cirri; five to seven left and three to five right marginal rows. Sequences of small subunit ribosomal DNA were determined from both species, and pairwise distances with their relatives were analyzed.

Bucklandiella araucana (Grimmiaceae), a new species from Chile

The new species Bucklandiella araucana Larrain is described from southern Chile. It is characterized by its small size, epilose, almost cucullate leaves, lack of a differentiated basal marginal row of pellucid and straight-walled cells, bistratose and dorsally flat costa at midleaf, smooth to slightly bulging lamina cells, unistratose leaf lamina with scattered bistratose spots at distal margins, undivided, prong-like peristome teeth, and deeply lobed calyptra. The species seems to be an endemic of the volcanic range of the western slopes of the southern Andes (39-42uS), where it grows in Nothofagus forests and open lava fields on the hillsides of the many active volcanoes of the area. Molecular data support the distinctiveness of this new taxon and identify Bucklandiella araucana as sister to B. curiosissima, B. didyma, and B. emersa. A distribution map and illustrations of the new species are presented. The phylogenetic perspectives of our novel molecular results are discussed.

Species of the Cocconeis peltoides group with a marginal row of unusual processes (Mascarenes and Kerguelen Islands, Indian Ocean)

Two diatoms related to Cocconeis peltoides Hustedt (Bacillariophyceae), from coral reef environments (Mascarenes, Western Indian Ocean), are proposed as a new Cocconeis variety and a new C. species: Cocconeis peltoides var. archaeana Riaux-Gobin et Compère and Cocconeis sigillata Riaux-Gobin et Al-Handal. Cocconeis peltoides and the two new taxa possess an unusual marginal row of small processes on their sternum valve, internally opening as curb-like structures. Several other Cocconeis species, encountered during sampling campaigns in Kerguelen (Southern Ocean, Indian Ocean sector), also share such processes, including Cocconeis hauniensis Witkowski and Cocconeis germainii Riaux-Gobin, Witkowski et Romero. The shared characteristics of these taxa are examined and compared in detail.

First Record of Two Urostyloid Ciliates (Spirotrichea: Urostylida: Urostyloidea) from Brackish Water in Korea

Two urostyloid ciliates, collected from brackish water in Korea, were identified as Diaxonella pseudorubra pseudorubra (Kaltenbach, 1960) Berger, 2006 and Pseudokeronopsis flava (Cohn, 1866) Wirnsberger, Larsen and Uhlig, 1987. The description was based on living, protargol impregnated specimens. These species are described as follows: Diaxonella pseudorubra pseudorubra: body size in vivo <TEX>$145-230{\times}40-60\;{\mu}m$</TEX>, elongated ellipsoidal in shape. Cytoplasm reddish and flexible. Adoral zone of membranelles occupied 30-40% of the body; composed of 33-44 membranelles; 1-3 frontoterminal cirri, 1-4 frontal row cirri, 4-6 buccal cirri, 6-10 transverse cirri. Midventral rows composed of 14-24 cirri, four left marginal rows, one right marginal row. Two kinds of cortical granules; the larger one is yellowish and the smaller one is reddish. Pseudokeronopsis flava: body size in vivo <TEX>$150-210{\times}30-45\;{\mu}m$</TEX>, elongated ellipsoidal shape. Cytoplasm yellowish and flexible. Adoral zone of membranelles occupied 25-30% of body; composed of 44-58 membranelles in number. Frontal cirri forming bicorona composed of 5-7 cirral pairs, 2-3 frontoterminal cirri, one buccal cirrus, and 2-3 transverse cirri. Midventral rows composed of 18-33 cirri, 34-53 left marginal cirri, and 40-58 right marginal cirri. Two kinds of cortical granules; the larger one is colorless and "blood-cell-shaped," and the smaller one is yellowish. Diaxonella pseudorubra pseudorubra is different from the most similar subspecies, D. pseudorubra pulchra, in cytoplasmic color and number of midventral cirri. Pseudokeronopsis flava is different from its most similar congeners in pigment granular color, number of bicorona, number of midventral cirri, and position of the contractile vacuole.

Descriptions of new species of the diverse and endemic land snail Amplirhagada Iredale, 1933 from rainforest patches across the Kimberley, Western Australia (Pulmonata: Camaenidae)

Descriptions of new species of the diverse and endemic land snail Amplirhagada Iredale, 1933 from rainforest patches across the Kimberley, Western Australia (Pulmonata: Camaenidae)

Morphology and Phylogeny of a New Urostylid Ciliate, Monocoronella carnea n. g., n. sp. (Ciliophora, Hypotricha) from Daya Bay, Southern China

The morphology, infraciliature and small subunit ribosomal RNA gene-based phylogeny of an urostylid ciliate, Monocoronella carnea n. g., n. sp., found in coastal areas off Daya Bay, Southern China, were investigated. The new genus Monocoronella n. g. is recognized by the following features: having conspicuous frontal cirri forming a long and single corona; buccal and frontoterminal cirri present; single marginal row on each side; adoral zone, midventral complex and transverse cirri in Pseudokeronopsis mode. The type species M. carnea n. sp. is diagnosed by the combination of marine habitat and brown-reddish color of the cortical granules. Phylogenetic analyses for the new taxon indicate that Monocoronella n. g. is most closely related to Bergeriella, and is located within the core Urostylida clade. A misidentification in previous literature was recognized and a new species, Monocoronella dragescoi n. sp. [Basionym: Holosticha (Keronopsis) monilata (Kahl 1928) sensu Dragesco (1970) et sensu Dragesco and Dragesco-Kernéis (1986), non sensu Kahl (1928)], was suggested.

New Record of Two Apokeronopsis Species (Ciliophora: Urostylida: Pseudokeronopsidae) from Korea

The morphology of the two marine hypotrichous ciliates Apokeronopsis bergeri and A. ovalis, isolated from the Yellow Sea, Korea, are described based on live and protargol-impregnated specimens. It is the first time that these species have been recorded in Korea. In addition, the small subunit ribosomal RNA gene was sequenced for comparison with the public database. The genus Apokeronopsis has recently been established in the family Pseudokeronopsidae, and the two congeners of the Korean population share the following characteristics: one row of one or more buccal cirri; usually two frontoterminal cirri; midventral complex composed of two distinctly separated rows; one left and one right marginal row; number of transverse cirri, more than eight; absence of caudal cirri; two types of cortical granules. Apokeronopsis bergeri differs from A. ovalis primarily in body shape (fusiform vs. oval form), size (usually <TEX>$260{\times}80{\mu}m$</TEX> vs. <TEX>$160{\times}55{\mu}m$</TEX>), type II cortical granules (oval vs. round shape; yellow-green vs. mostly colourless and only a few yellow-green in colour), and morphometric data (75-106 vs. 53-70 in adoral membranelles; 37-47 vs. 24-36 in frontal cirri; 9-15 vs. 1-2 in buccal cirri), as well as molecular data (2.87% of pairwise distance).

Evolution of discocephalid ciliates: Molecular, morphological and ontogenetic data support a sister group of discocephalids and pseudoamphisiellids (Protozoa, Ciliophora) with establishment of a new suborder Pseudoamphisiellina subord. n.

Discocephalids and pseudoamphisiellids are possibly two of the most confused groups among hypotrichous/euplotid ciliates regarding their systematic position and phylogenetic relationships. The former were often regarded as related to euplotids while the latter, in the absence of molecular data, were mostly assigned to the urostylid-like hypotrichs. In the present work, the small subunit rRNA genes of several rarely observed discocephalid and pseudoamphisiellid genera were analyzed to obtain insights into the phylogenetic relationships of these highly ambiguous Spirotrichea. Four different tree reconstruction algorithms yielded nearly identical topologies, which indicated both groups belong to the same assemblage. This assemblage is clearly isolated as a deep-branching clade and invariably positioned between Euplotida and Hypotricha. The sister group relationship of the Pseudoamphisiellidae and Discocephalidae supports the previous suggestion that they might represent an ordinal taxon, the Discocephalida. Both morphological and morphogenetic features indicate that the pseudoamphisiellids should be placed in the order Discocephalida but as a sister group to other typical discocephalids. Thus we propose establishing a new suborder, Pseudoamphisiellina subord. n. The new taxon is diagnosed by the following characteristics: (i) two distantly separated midventral rows that are morphogenetically formed with an urostylid mode; (ii) absence of the "frontoterminal row", which is formed from the posterior-most frontoventral-transverse cirral anlage in all other typical urostylids; (iii) numerous caudal cirri that derive from each of the dorsal kinety anlagen; (iv) right marginal row that has a unique de novo origin; and (v) inhabiting periphytic communities. The validity of the suborder Pseudoamphisiellina is firmly supported by molecular data.

Morphology and Small Subunit (SSU) rRNA Gene Sequence of the New Brackish Water Ciliate Neobakuella flava n. g., n. sp. (Ciliophora, Spirotricha, Bakuellidae) and SSU rRNA Gene Sequences of Six Additional Hypotrichs from Korea

The morphology and the small subunit (SSU) rRNA gene sequence of the hypotrich Neobakuella flava n. g., n. sp. from the estuary of the Taehwagang River (Ulsan, South Korea) were investigated. The three frontal cirri, the composition of the midventral complex of cirral pairs and rows, and the simple dorsal kinety pattern of three bipolar kineties assign it to the urostyloid taxon Bakuellidae. The increased number of buccal and parabuccal cirri, the presence of transverse cirri, and more than one left marginal row, as well as the lack of caudal cirri separate Neobakuella n. g. from the other bakuellids. Neobakuella flava n. sp. has many 0.3 μm sized green and/or yellow usually dark-green cortical granules and some sparsely distributed, 2 × 1 μm sized grass green with yellowish shimmer granules. The gene sequence data indicate a close relationship with Diaxonella and a distinct separation from the bakuellid Metaurostylopsis and parabirojimid Parabirojimia. The SSU rRNA gene sequences of four further urostyloids (i.e. Diaxonella pseudorubra, Anteholosticha monilata, Metaurostylopsis struederkypkeae, Pseudourostyla cristata) and two stylonychines (i.e. Sterkiella cavicola, Sterkiella histriomuscorum) from Korea were analyzed. Anteholosticha monilata, type of the genus, is clearly separated from the Holosticha clade, supporting the morphological separation from Holosticha. Sterkiella cavicola, type of Sterkiella, clusters within the stylonychines and is obviously closely related with S. histriomuscorum.

Morphology and Small Subunit rDNA Phylogeny of a New Soil Ciliate, Bistichella variabilis n. sp. (Ciliophora, Stichotrichia)

We isolated a new ciliate, Bistichella variabilis n. sp., from slightly saline soil of the Yellow River Delta in China and studied it using live observation, protargol staining, and small subunit (SSU) rRNA gene sequencing. Bistichella variabilis is elongated ellipsoidal and about 220 × 70 μm in vivo, with a variable number and arrangement of cirri- ventral row VI mostly very short, but a long row observed also in one specimen, and an extra row occasionally exists besides the left or the right marginal row. Bistichella variabilis differs from all congeners except Bistichella buitkampi (Foissner, 1982) in the macronuclear pattern (four vs. two or many nodules); and from B. buitkampi by the usual oblique arrangement of transverse cirri (vs. perpendicular); and the ventral row VI mostly restricted in the posterior quarter of the cell (vs. long and stretching to the anterior quarter). Phylogenetic analyses of SSU rDNA sequences indicated that B. variabilis grouped with the clade of Orthoamphisiella breviseries and Uroleptoides magnigranulosus with high support values. Despite their distinct differences in morphology, these three species have sequence similarities of 99.5-99.7%. Nonetheless, it is still premature to assign Bistichella together with Uroleptoides to the family Orthoamphisiellidae because of the taxonomic uncertainties and undersampling.

First Records of Two Aquatic Oxytrichid Ciliates (Ciliophora: Sporadotrichida: Oxytrichidae) from Korea

For investigation of the Korean ciliate fauna, two oxytrichid ciliates, Histriculus histrio (Muller, 1773) and Sterkiella thompsoni Foissner, 1996, were collected from freshwater and brackish waters in South Korea, respectively. These two ciliates are reported for the first time in Korea. Descriptions were based on observations of live and silver stained specimens. Diagnoses of these species are as follows. Histriculus histrio: body is approximately <TEX>$190{\times}85\;{\mu}m$</TEX> in size, almost ellipsoidal in shape, posterior part rather thin and very translucent. Cortical granules are absent. Both marginal rows are almost confluent at the posterior end. Six dorsal kineties are present. Sterkiella thompsoni: body is approximately <TEX>$140{\times}50\;{\mu}m$</TEX> in size. Body margins are usually in parallel. Cortical granules are absent. Invariably, four dorsal kineties are present. Two caudal cirri are located on the dorsal surface. Three ellipsoidal macronuclear nodules are present.

Characterization of two urostylid ciliates, Metaurostylopsis flavicana spec. nov. and Tunicothrix wilberti (Lin &amp; Song, 2004) Xu et al., 2006 (Ciliophora, Stichotrichia), from a mangrove nature protection area in China

Two marine stichotrich ciliates, Metaurostylopsis flavicana spec. nov. and Tunicothrix wilberti (Lin & Song, 2004) Xu et al., 2006, isolated from the Shenzhen Mangrove Protection Area on the coast of the South China Sea, were investigated using live observation and protargol impregnation techniques. Metaurostylopsis flavicana is characterized by its elongate body shape, yellowish body colour and bright-yellow cortical granules that are either grouped around the cirri and the dorsal cilia or aligned between the rows of cirri and dorsal cilia. It has four to eight frontal, two frontoterminal, one buccal and seven to ten transverse cirri, a mid-ventral complex comprising 13-17 midventral cirral pairs in a row that extends about three-fifths of the body length, four left and three right marginal rows and three complete dorsal kineties. The small subunit rRNA gene of this species was sequenced and phylogenetic trees were constructed in which M. flavicana does not group with its congeners, suggesting that the genus Metaurostylopsis is paraphyletic. Some supplementary morphological and morphogenetic traits for Tunicothrix wilberti are also documented.

Ontogeny and phylogeny of Metaurostylopsis cheni sp. n. (Protozoa, Ciliophora), with estimating the systematic position of Metaurostylopsis

Chen, X., Huang, J. &amp; Song, W. (2010). Ontogeny and phylogeny of Metaurostylopsis cheni sp. n. (Protozoa, Ciliophora), with estimating the systematic position of Metaurostylopsis. —Zoologica Scripta, 40, 99–111.The ciliate genus Metaurostylopsis seems to be a highly divergent marine‐habiting group, of which neither systematic position nor the variation of their ontogeny has been critically checked. In the present work, the morphology and morphogenesis during asexual division of a new form, Metaurostylopsis cheni sp. n., isolated from the Yellow Sea, China, were investigated and comparison among known congeners was performed. The new species has two types of cortical granules, the larger ones of which are flattened and oval or circular in outline with a longitudinal groove, yellow–green in colour, and arranged along the cirral rows and dorsal kineties, whereas the smaller ones are colourless or grayish and sparsely distributed. The main morphogenetic features are: (i) the entire parental ciliature, including the old oral apparatus, is renewed, (ii) the oral primordium of the proter originates de novo and beneath the surface of the buccal cavity, that is, sub‐apokinetally, (iii) the anlagen of the marginal rows and of the dorsal kineties are formed intrakinetally and (iv) fusion of the macronuclear nodules results in an irregular mass with only few branches. The small subunit ribosomal RNA (SSU rRNA) gene of M. cheni was sequenced. Phylogenetic analysis based on SSU rRNA gene sequence data shows that M. cheni clusters with all other Metaurostylopsis spp. sequenced to date indicating that the genus is monophyletic and is probably closely related to the Apokeronopsis–Thigmokeronopsis‐group, within the order Urostylida.

Morphological and phylogenetical studies on a new soil hypotrich ciliate: Kahliella matisi spec. nov. (Hypotrichia, Kahliellidae)

The morphology, ontogenesis, encystment, and 18S rRNA gene sequence of a new soil hypotrich ciliate, Kahliella matisi, were studied. Main characteristics of K. matisi are: (1) two short and six longitudinal cirral rows right of the adoral zone of membranelles and four longitudinal rows left of it; (2) three dorsal kineties, of which kinety 1 extends along the left cell margin, kinety 2 runs in a slightly sigmoidal line, and kinety 3 is distinctly shortened posteriorly. Ontogenesis is similar to that in congeners, especially in the development of the marginal rows and long dorsal kineties, the preservation of some old cirral rows after division, and the direction of the neokinetal wave. However, there are some peculiarities: (1) reorganization of the proximal parental adoral membranelles; (2) splitting of opisthe's anlage II into the cirral streak II and III; and (3) formation of the parental cirral row R3 from anlagen IV and V. During encystment, the body diminishes and becomes globular, the nuclear apparatus is reorganized, and the ciliature is resorbed. In our molecular phylogenies, the family Kahliellidae is polyphyletic and the position of K. matisi is rather poorly resolved, indicating a relationship with oxytrichids.

Taxonomy and phylogeny of Tunicothrix (Ciliophora, Stichotrichia), with the description of two novel species, Tunicothrix brachysticha n. sp. and Tunicothrix multinucleata n. sp., and the establishment of Parabirojimidae n. fam.

The morphology and molecular phylogeny of two novel urostylid ciliates, Tunicothrix brachysticha n. sp. and Tunicothrix multinucleata n. sp., were investigated using the techniques of living observation, protargol impregnation and small-subunit rRNA gene sequencing. Both species were found to be frequent in muddy-sand sediment but very rare in sandy sediment of the intertidal zone of Qingdao Bay, China. Tunicothrix brachysticha is about 90 × 30 µm in vivo, with a broadly clavate body shape, and is characterized by a rather short midventral row terminating at 40 % of the body length and a right marginal row 1 terminating at mid-body. Tunicothrix multinucleata is about 190 × 30 µm in vivo, and is characterized by a clavate body shape and the presence of 7-10 macronuclear nodules. Phylogenetic analyses showed that Tunicothrix clustered robustly with Parabirojimia, forming a clade that branches from the Urostylida core clade with high bootstrap values. Based on the morphological and molecular data, we establish a new family, Parabirojimidae n. fam., which comprises Parabirojimia and Tunicothrix and is distinguished by a unique, roughly T-shaped bipartite adoral zone of membranelles, three enlarged frontal cirri and a midventral complex with midventral pairs confined to the buccal field.

Trigonotarbid arachnids from the Lower Devonian (Lower Emsian) of Alken an der Mosel (Rhineland-Palatinate, SW Germany)

New material of the trigonotarbids Alkenia and Archaeomartus from the Lower Devonian type locality Alken an der Mosel/Germany is described. Stormer’s original description of Alkenia is essentially confirmed and supplemented. The genus is placed in Aphantomartidae. In contrast to earlier accounts, we show that Archaeomartus has an anterior diplotergite and a longitudinally three-divided posteriormost (ninth) tergite. The new family Archaeomartidae is proposed. Whether a marginal row of larger tubercles on the opisthosoma can be recognized is strongly influenced by the taphonomic history of the fossil, and sexual dimorphism may also be involved. Thus, we propose that Archaeomartus levis and A. tuberculatus, which can be discriminated solely by the presence or absence of this feature, are synonyms. Furthermore, morphological similarity suggests the possibility that archaeomartids, with their opisthosomal tergites divided into three plates, gave rise to the later (Carboniferous) anthracomartids, specifically through the division of the lateral plates and the ninth tergite. Finally, our reassessment of Archaeomartus shows that ‘A.’ roessleri Dunlop and Brauckmann, 2006 can no longer be adequately maintained in this genus. This younger species from the early Upper Carboniferous of Hagen-Vorhalle, Germany, is reassigned to Namurotarbus n. gen. as Namurotarbus roessleri n. comb.

New Record of Two Species in Stichotrichous Ciliates (Ciliophora: Stichotrichia) from Korea

Two stichotrichous ciliates, Amphisiella annulata (Kahl, 1928) and Pseudoamphisiella alveolata (Kahl, 1932), were collected from the Yellow Sea in Incheon, Korea and were identified as new to Korea. The main diagnostic key to the species of the genera are that the two species share the features of two macronuclear nodules, one marginal row per side, and transverse cirri. A. annulata is distinguishable from other members in the genus mainly due to the several ring-shaped (hollow) structures in its cytoplasm and its wide and narrowly arranged amphisiellid median cirral row. P. alveolata has a conspicuous alveolar layer and two conspicuous macronuclear nodules, but no frontoterminal cirri.

Phylogenetic analyses suggest thatPsammomitra(Ciliophora, Urostylida) should represent an urostylid family, based on small subunit rRNA and alpha-tubulin gene sequence information

The morphologically unique ciliate Psammomitra has long been considered as a systematically uncertain stichotrich. This is mainly because of its highly specialized morphology and a lack of either detailed information concerning its ontogenesis, or molecular data. Based on the small subunit rRNA (SSrRNA) gene and alpha-tubulin gene sequences, we re-evaluated the phylogenetic position of Psammomitra retractilis using multiple algorithms. Phylogenetic trees inferred from the SSrRNA gene sequences representing a total of 53 spirotrichs demonstrated the closest relationship of Psammomitra was with Holosticha-like taxa, with strong support, which clearly suggested that Psammomitra should be placed into the order Urostylida although it branched at a rather deep level, and is likely to be closely related to Holostichidae. With consideration to molecular evidence and morphological characters, Psammomitra should be a clearly outlined taxon at about the rank of family, i.e. Psammomitridae stat. nov., within the order Urostylida. The improved diagnosis for this family is as follows: Urostylida possessing extremely contractile, elongated body which consists of three parts: head, trunk, and slender tail; midventral complex composed of midventral pairs only and restricted to about anterior 1/3 of ventral surface; frontal, frontoterminal, and transverse cirri present; one left and one right marginal rows which commence near proximal end of adoral zone and extend to near rear body end.