Morphogenesis of the marine spirotrichous ciliate, Trachelostyla pediculiformis (Cohn, 1866) (Ciliophora, Stichotrichia), with consideration of its phylogenetic position

The cortical development during binary fission of the relatively poorly known stichotrich ciliate, Trachelostyla pediculiformis (Cohn, 1866) Borror, 1972, found in coastal waters near Qingdao, China, was investigated using the protargol impregnation method. The morphogenetic process reveals some pretty unusual characteristics, which do not follow the Oxytricha-pattern: (1) the parental oral apparatus is entirely renewed from an oral primordium formed de novo in the proter; (2) in the proter, the parental undulating membranes are not involved in the formation of the newly formed oral primordium; both undulating membrane-anlagen (UM-anlage) and frontoventral-transverse cirral anlagen (FVT-anlagen) develop from the oral primordium in the proter; (3) the dorsal kineties (DK) are generated in a unique way, that is, in both dividers, two separate groups of DK-anlagen develop in the right- and left-most DK, generate all the DK and evolve to replace the old structures; (4) three caudal cirri are formed at the posterior ends of three right-most dorsal kinety anlagen; (5) eight frontal, five ventral and five transverse cirri are derived from six streaks, namely, the UM-anlage and 5 FVT-anlagen; the cirri are segregated from these anlagen in the pattern 1:3:3:3:4:4 (from left to right) in the Oxytricha mode. Based on both SSrRNA gene sequencing and morphogenetic data, the systematic positions of the genus Trachelostyla Borror, 1972 as well as the family Trachelostylidae Small and Lynn, 1985 are briefly analyzed. The results indicate that this genus/family could be a highly isolated lineage and might be ancestral to other well-known oxytrichids.     

Morphology and morphogenesis of Holosticha heterofoissneri nov. spec. from the Yellow Sea,China (Ciliophora,Hypotrichida)

The morphology and morphogenesis of the marine hypotrichous ciliate Holosticha heterofoissneri nov. spec. from mollusc culture in Qingdao, China are described based on living and protargol-impregnated specimens. The new species is characterized by: adoral zone slightly bipartite, consisting of on average 43 membranelles; constantly 5 dorsal kineties, and 12 pairs of cirri in midventral rows, and 14–16 macronuclear segments, which differs from the closely related species, H. foissneri. Its morphogenetic process shows the following features: (1) the parental AZM is retained unchanged and will be inherited by the proter, only the old UM reorganized; (2) FVT-cirral anlagen in both division parts derive from the breaking of primary primordia; (3) during the formation of FVT-cirral anlagen, most midventral cirri remain intact; and there appears an 'extra' anlage (EA) between the UMA and other FVT-cirral primordia; (4) the generation type of the dorsal kineties is of 'one group mode', the leftmost one of the 4 primordia fragmentates to form a new kinety; (5) at the early stage of morphogenesis, replication bands of macronuclear segments are apparently present.     

Description of the Rare Marine Ciliate, Uronychia multicirrus Song, 1997 (Ciliophora; Euplotida) based on Morphology, Morphogenesis and SS rRNA Gene Sequence

ABSTRACT. A population of the marine euplotid ciliate, Uronychia multicirru s Song 1997 , found in the littoral zone of the Daya Bay, Guangdong, South China, was investigated using live observation and protargol impregnation method. This species is diagnosed by possessing a long row of ventral cirri, which has never been seen in all other known congeners. Divisional process, described based on protargol-impregnated specimens, is typical of the genus regarding its general pattern: (1) the oral primordia in both proter and opisthe develop de novo in two subcortical pouches, while the UM-anlage forms de novo (i.e. does not develop from the oral primordium); (2) five frontoventral-transverse (FVT)-cirral anlagen develop in a primary-mode on the cell surface, and almost all the cirri are derived from the FVT-anlagen, except the first frontal cirri, which are formed de novo in both dividers; (3) the species characteristic ventral row derives from the right-most FVT-anlage; (4) the parental structures do not take part in the construction of the marginal anlagen, and (5) the caudal cirri originate in the right-most two dorsal kineties in a multi-segmentation mode. The small subunit rRNA gene of U. multicirrus (GenBank accession number: EU267929) is 1,773 bp and differs by 0.9–1.41% from its closely related congeners.     

Morphology,morphogenesis and molecular phylogeny of a freshwater ciliate,Monomicrocaryon euglenivorum euglenivorum (Ciliophora,Oxytrichidae)

The morphology, morphogenesis and molecular phylogeny of the oxytrichid ciliate, Monomicrocaryon euglenivorum euglenivorum (Kahl, 1932) Foissner, 2016, isolated from freshwater in a seaside park, Guangzhou, China, were investigated. Monomicrocaryon euglenivorum euglenivorum can be recognized as follows: caudal cirri in midline of body; dorsal kinety 1 without a one-kinetid-wide gap; transverse cirri acicular or rod-shaped with a fringed distal end; right marginal row commences at level of buccal vertex or anterior to buccal vertex. The main events during binary fission are as follows: (1) the proter retains the parental adoral zone of membranelles entirely; (2) frontoventral-transverse cirral anlagen I–VI are segmented in the ordinary pattern 1:3:3:3:4:4 from left to right, which form three frontal, four frontoventral, one buccal, three postoral ventral, two pretransverse ventral and five transverse cirri, respectively; (3) dorsal morphogenesis is in the typical Oxytricha-pattern, but fragmentation of dorsal kinety 3 is indistinct; and (4) three caudal cirri are formed, one at the posterior end of each of dorsal kineties 1, 2 and 4. Phylogenetic analyses based on SSU rDNA sequences showed that M. euglenivorum euglenivorum clustered with Kleinstyla dorsicirrata and Heterourosomoida lanceolata rather than with its congener M. elegans. The genus Monomicrocaryon is not monophyletic in this study; however, its monophyly is not rejected by the AU test.     

Morphology,Morphogenesis and Molecular Phylogeny of a New Obligate Halophile Ciliate,Schmidtiella ultrahalophila gen. nov., spec. nov. (Ciliophora,Hypotrichia) Isolated from a Volcanic Crater on Sal (Cape Verde Islands)

A new hypotrichous ciliate, Schmidtiella ultrahalophila gen. nov., spec. nov., was isolated from a solar saltern on the island of Sal, Cape Verde. The possession of only one short dorsal kinety clearly distinguishes S. ultrahalophila from other known hypotrichous genera and species. Further diagnostic characters include: a flexible and slender body, an average size of 85 × 15 μm in vivo; a bipartite adoral zone with two hypertrophied frontal adoral membranelles and nine to twelve ventral adoral membranelles; three frontal, one parabuccal, two frontoventral, two or three postoral ventral, and two or three frontoterminal cirri; and marginal cirral rows variable in number, usually one on each side. Ontogenetic data indicate the following: the frontal‐ventral cirri originate from six or five anlagen; the proter inherits the parental adoral zone; the frontal and ventral cirri originate from five or six anlagen; and the marginal cirral rows and the dorsal kinety tend to originate intrakinetally. Additional marginal rows are rarely derived from de novo anlagen. Based on its morphology, morphogenesis and its SSU rRNA phylogenetic placement, the new species should be assigned to the order Sporadotrichida Fauré‐Fremiet, 1961. Due to low taxon sampling, however, its exact position in this order remains enigmatic.     

变藓棘毛虫的形态学重描述及细胞发生学研究

通过活体观察和蛋白银染色法对采自青岛沙滩半咸水的变藓棘毛虫Sterkiella histriomuscorum(纤毛门, 腹毛目)进行了形态学及细胞发生学研究。该种群形态学与前人报道的土壤及淡水种群基本一致: 虫体近长椭圆形, 活体大小约(100-160) m (40-75) m; 无皮层颗粒; 2938片口小膜; 额棘毛3根; 额腹棘毛4根; 口后腹棘毛3根; 横前腹棘毛2根; 横棘毛3-5根; 左右缘棘毛列分别由17-23、20-24根棘毛组成; 6列背触毛; 2枚大核。其主要发生学特征如下: (1)老口围带完全保留, 老波动膜解体重建; 后仔虫口原基独立发生; (2)额腹横棘毛为5原基次级发生式, 部分原基来自老棘毛解体, 以2:3:3:4:4方式分化为新棘毛; (3)缘棘毛原基产生于老结构中, 并向两极延伸逐渐形成前后仔虫的新结构; (4)背触毛发生为典型Oxytricha模式; (5)大核在发生过程中完全融合。研究对首次在半咸水生境中发现的变藓棘毛虫种群进行了活体形态学和纤毛图式描述, 补充了显微照片、性状统计数据及发生过程的细节信息。       

Morphologie und Morphogenese des Bodenciliaten Oxytricha granulifera sp.n. (CiIiophora, Oxytrichidae)

Oxytricha granulifera sp.n. differs from other members of the genus by its subpellicular granules and the strongly shortened dorsal kinety 4. The overall pattern of the morphogenetic events is similar to that known from other Oxytrichidae. However, the oral primordium evolves de novo between the left marginal cirral row and the postoral cirri. The six anlagen of the frontoventral cirri are of different origin. Two anlagen of the proter evolve from parental frontal cirri, two from the opisthe, and one includes basal bodies of the proter and opisthe. Two anlagen of the opisthe evolve from the oral primordium, and three primordia originate from the postoral cirri. Frontal cirrus 1 evolves from the paroral membrane in the proter, and from the oral primordium and the anlagen of the frontoventral cirri in the opisthe. The genus Oxytricha can be subdivided into several groups with regard to the origin of its oral primordium and the development of the frontoventral cirri. The morphogenesis of the dorsal kineties in the Hypotrichida is reviewed. Seven different modes of origin are distinguished. We conclude that morphogenetic features cannot be used in the classification of the Hypotrichida at the generic level, because we have too little information to decide whether special morphogenetic features are important at the generic or species level.     

Morphology,ontogeny and molecular phylogeny of a new urostylid ciliate,Bakuella (Pseudobakuella) guangdongica n. sp. (Ciliophora,Hypotrichia) from southern China

The morphology, morphogenesis, and molecular phylogeny of Bakuella (Pseudobakuella) guangdongica n. sp., isolated from southern China, were investigated. The new species is characterized by a body length of 150–225 μm in vivo; 35–42 adoral membranelles; 3–5 buccal, two frontoterminal, 7–12 transverse and two pretransverse ventral cirri; midventral complex comprised of 10–20 pairs and two rows extending to transverse cirri; posterior part of marginal rows slightly overlapping; colorless cortical granules about 1 μm across, arranged in small groups; soil habitat. Its main ontogenetic features are: (1) in the proter, the parental adoral zone of membranelles is completely renewed by new structures; (2) in the opisthe, the oral primordium originates apokinetally, some old midventral cirri join the formation of frontoventral-transverse cirral anlagen; (3) the anlagen for marginal rows and dorsal kineties develop intrakinetally; and (4) the numerous macronuclear nodules fuse into a single mass before dividing. Phylogenetic analyses based on the SSU rDNA sequence suggest the non-monophyly of the genus Bakuella.     

钩刺斜管虫无性生殖期间的口纤毛器及细胞发生研究（原生动物：纤毛虫）

钩刺斜管虫口和体纤毛器演化模式是研究该类动物个体发生的优秀模型。通过跟踪研究,澄清了后仔虫口器发生以及体纤毛器起源上的几点疑问,并证实：体左侧二列片段动基列为同源再造而非来自老结构的分裂或复制;三列围口纤毛均为双动基列构造;后仔虫口原基场的构建系由５列体动基列共同参与完成的,其中最左侧两列短的原基片段与原基１整合为一体,从而发展成营养期虫体的外围口动基列;后仔虫背触毛原基为独立发生。     

Morphology and Morphogenesis of a Novel Saline Soil Hypotrichous Ciliate,Gonostomum sinicum nov. spec. (Ciliophora,Hypotrichia, Gonostomatidae), Including a Report on the Small Subunit rDNA Sequence

Morphology, cirral pattern, and morphogenesis of the new saline soil hypotrich, Gonostomum sinicum nov. spec. collected from Longfeng Wetland in Daqing, north China, were studied, using detailed live observations and protargol‐stained specimens. The new species is characterized as follows: (i) a size in vivo of 100–125 × 30–40 μm, (ii) colorless cortical granules, 0.5 μm across, arranged in short rows, (iii) an adoral zone composed of 28–33 membranelles, (iv) three or four frontoventral rows, one of which extends onto the postoral area, (v) left and right marginal rows composed of 18–27 and 21–35, cirri, respectively, and (vi) usually two transverse cirri. Morphogenesis is as usual for the genus Gonostomum, i.e. the cirral primordia II–VI are primary primordia which split into two sets for proter and opisthe in division middle stages, except for anlage I which develops independently. However, the number of frontoventral transverse anlagen is either five or six not only in different individuals but even in proter and opisthe of the same divider. The phylogenetic analyses based on SSU rDNA sequences showed that the genus Gonostomum is nonmonophyletic, indicating that the patterns of cirri and dorsal kineties are homoplasious characters. The new species G. sinicum nov. spec. is perhaps closely related to Cotterillia bromelicola and two congeners.     

Cortical structure in non-dividing and dividing Diophrys japonica spec. nov. (Ciliophora, Euplotida) with notes on morphological variation

The morphology and morphogenesis of Diophrys japonica spec. nov., isolated from the Mie Port, Nagasaki, Japan, were investigated from life and following impregnation with protargol. The new species is recognized by the following characters: Body elliptical in outline and slightly greyish to yellowish in color; size in vivo about 80-120 x 50-70 microm; pellicle flexible, with underlying granules densely arranged in lines; ciliature comprising about 30-46 adoral membranelles, 4-7 frontal, 1-4 ventral and 4-7 transverse cirri, always 1 left marginal and 3 caudal cirri, and 4 dorsal kineties; usually two macronuclear nodules; fragment kinety with 2-5 dikinetids; marine habitat. The main morphogenetic events are: (1) the opisthe's oral primordium develops de novo in a subsurface pouch near the left transverse cirri; (2) the proter retains the parental AZM except for reorganization of some proximal membranelles; (3) cirral anlagen for the frontal, ventral and transverse cirri in both dividers develop separately from the oral primordium or parental cirri, and are derived from the separation of primary primordia that originate de novo; (4) the anlagen for the left marginal cirrus and fragment kinety also form de novo and separately; (5) dorsal kinety anlagen occur within the parental structures at mid-body and posterior end of the cell, of which the right-most one contributes three caudal cirri from its posterior portion. Based on available ontogenetic data, the author proposes that the numbers of left marginal and caudal cirri can be regarded as reliable characters for species identification, while the numbers of frontal, ventral and transverse cirri are not consistent enough for species distinction. A key to the eleven adequately known species of Diophrys is presented.     

Morphology,Morphogenesis, and Molecular Phylogeny of Paraparentocirrus sibillinensis n. gen., n. sp., a “Stylonychine Oxytrichidae” (Ciliophora,Hypotrichida) Without Transverse Cirri

A terrestrial oxytrichid ciliate Paraparentocirrus sibillinensis n. gen., n. sp., which was found in soil samples of a beech forest stand within the National Park of Sibillini Mountains, Italy, was investigated using live observation and protargol impregnation. The morphology of interphase, morphogenesis, and molecular phylogeny inferred from SSU rDNA sequences of this ciliate were studied. Paraparentocirrus n. gen., is mainly characterized by a semirigid body, an undulating membrane in the Oxytricha pattern, six fronto‐ventral (FV) rows, the absence of transverse cirri, one right and one left row of marginal cirri, four dorsal kineties, two dorsomarginal rows, and caudal cirri at the end of dorsal kinety 4. During morphogenesis, oral primordia develop through the proliferation of basal bodies from some cirri of FV rows 4 and 5, and FV row 6 takes part in the anlagen formation of the proter. The dorsal morphogenesis was typical of oxytrichids, with simple fragmentation of dorsal kinety 3, and the dorsomarginal rows developed from the right marginal row. Phylogenetic analyses based on the SSU rDNA sequences support the classification of this new genus in the stylonychines.     

A redescription of the oxytrichid Tetmemena pustulata () and notes on morphogenesis in the marine urostylid Metaurostylopsis salina Lei et al., 2005 (Ciliophora,Hypotrichia)

Two hypotrichous ciliates from China were investigated. The common oxytrichid species Tetmemena pustulata (Müller, 1786) Eigner, 1999, isolated from the estuary of the Pearl River in southern China, was investigated with emphasis on its living morphology and infraciliature. Tetmemena pustulata is characterized as follows: body elliptical to obovoid in shape; 75–115 × 40–60 μm in vivo; two macronuclear nodules and two micronuclei; one contractile vacuole left of midline and somewhat ahead of midbody positioned; three frontal, four frontoventral, one buccal, three postoral ventral, two pretransverse ventral and five transverse cirri; cirrus III/2 ahead of level of cirrus IV/3; cirrus IV/2 arranged more anteriorly than cirrus V/4; transverse cirri not forming two distinct groups; three prolonged and widely separated caudal cirri; six dorsal kineties in Oxytricha-pattern with dorsal kineties 3 and 4 bipolar. The marine urostylid species Metaurostylopsis salina Li et al., 2005, isolated from an aquarium in Qingdao, northern China, was investigated with emphasis on its morphogenesis which is characterized by the de novo formation of the oral primordium in the proter and the development of the marginal rows from two anlagen that form within each parental structure separately in both dividers.     

Morphogenesis of a unique pseudourostylid ciliate,Trichototaxis songi (Ciliophora,Urostylida)

Divisional morphogenesis in the freshwater spirotrichous ciliate, Trichototaxis songi Chen et al., 2007, was investigated. The main morphogenetic events are characterised as follows: (1) the parental oral apparatus is completely renewed by the independently formed oral primordium in the proter; (2) the oral primordium in the opisthe is formed on the cell surface; (3) several left cirri of the midventral pairs participate in the formation of the oral primordium in the opisthe; (4) FVT-anlage I forms the leftmost pair of the bicorona; (5) the macronuclear nodules fuse into many masses rather than a single or branched mass as described in most pseudokeronopsids; and (6) usually, two marginal anlagen develop within each left marginal row separately. However, the number of left marginal anlagen is highly variable, even differing between the proter and opisthe of the same divider. The increase in the number of left marginal anlagen is by de novo generation of small anlagen to the left of the intrakinetal left marginal anlage, whereas the decrease in number is by resorption of the old marginal row(s). We posit that Trichototaxis is an intermediate form between the Pseudourostylidae and Pseudokeronopsidae as it shares morphogenetic features with both. Additionally, as in Uroleptopsis (Uroleptopsis), FVT-anlage I forms the leftmost pair of the bicorona in Trichototaxis indicating these genera may be closely related.     

Morphology,morphogenesis and molecular phylogeny of a novel soil ciliate,Afrokahliella paramacrostoma n. sp. (Ciliophora,Hypotrichia)

A soil hypotrich ciliate, Afrokahliella paramacrostoma n. sp., was discovered in China. Its morphology, morphogenesis and molecular phylogeny were investigated using standard methods. The new species is characterized as follows: body about 140–180 × 60–70 μm in vivo, cortical granules absent, contractile vacuole positioned about 40% down length of body, 5–9 macronuclear nodules, 34–49 adoral membranelles, 3–5 buccal and 3–6 parabuccal cirri, usually two frontoventral rows, three or four left and two or three right marginal rows, three dorsal kineties and one dorsomarginal kinety; 1–3 and one or two caudal cirri located at the ends of dorsal kineties 1 and 2, respectively. The ontogenetic process is characterized by: (1) the marginal anlagen on each side develop in the outer right and the inner left marginal rows, respectively; (2) five frontoventral-transverse cirral anlagen, anlagen II–IV develop in secondary mode; (3) dorsal morphogenesis follows a typical Urosomoida-pattern, no parental dorsal kineties are retained; (4) caudal cirri are generated at the ends of dorsal kineties 1 and 2. Phylogenetic analyses based on SSU rDNA sequence data reveals that Afrokahliella paramacrostoma n. sp. is closely related to Parakahliella macrostoma and Hemiurosomoida longa.     

Morphology,ontogeny and molecular phylogeny of a new brackish water ciliate Bakuella subtropica sp. n. (Ciliophora,Hypotricha) from southern China

This paper investigates the morphology, ontogenesis and small subunit (SSU) rRNA gene-based phylogeny of a new urostylid ciliate, Bakuella subtropica sp. n., discovered from the estuary of the Pearl River in Guangzhou, southern China. The new species is diagnosed by its elongate body, one buccal and one parabuccal cirrus, midventral complex comprised of 9–23 midventral pairs and one or two midventral rows extending to four fifths of body length, yellow-brown to yellow-greenish cortical granules and an estuary habitat. Its main ontogenetic features are: (1) in the proter, the parental adoral zone of membranelles is completely renewed by new structures and old midventral pairs join the formation of frontal-midventral-transverse cirral anlagen (FVT-anlagen); (2) in the opisthe, the oral primordium originates apokinetally, FVT-anlagen are formed besides and some old midventral cirri join the formation; (3) the anlagen for marginal rows and dorsal kineties develop intrakinetally; and (4) the numerous macronuclear nodules fuse into a single mass before dividing. Based on the SSU rDNA sequences, phylogenetic analyses show a close relationship between Bakuella subtropica sp. n., Apobakuella and Neobakuella, forming a clade separated from the other genera in the family Bakuellidae. Available morphological and ontogenetic data challenge the monophyly of Bakuellidae.     

Morphogenesis of the marine ciliate, Pseudoamphisiella alveolata (Kahl, 1932) Song & Warren, 2000 (Ciliophora, Stichotrichia, Urostylida) during binary fission

Morphogenesis during the binary fission of the stichotrich ciliate Pseudoamphisiella alveolata, isolated from Jiaozhou Bay near Qingdao, China, was investigated using protargol silver impregnation. The process is characterized as follows: (1) in the proter, only the posterior part of the parental adoral zone of membranelles is renewed, where the membranelles dedifferentiate and then rebuild the UM-anlage and the missing membranelles, (2) the oral primordium in the opisthe and the FVT-anlagen in both dividers are formed de novo on the cell surface, (3) an "extra" anlage, which is generated on the right of the right marginal anlage, develops into three or four "extra" marginal cirri that connect the caudal cirri with the marginal rows, (4) the right marginal anlage is formed within the old structure, (5) the FVT-cirri develop in a primary mode, and (6) unlike most stichotrichs, the right marginal anlagen in both dividers generate closely together. As an additional contribution, the diversity of morphogenetic patterns within the genus Pseudoamphisiella is discussed. Based on both morphogenetic and SS rRNA gene sequencing data, the systematic position of the genus Pseudoamphisiella as well as the family Pseudoamphisiellidae Song et al. 1997 is briefly analyzed. The results indicate that they should very possibly represent a higher evolved group in the order Urostylida.     

Morphological,Biometric, and Morphogenetic Comparison of Two Closely Related Species,Stylonychia vorax and S. pustulata (Ciliophora: Oxytrichidae)1

Differences in the morphology of Stylonychia vorax Stokes, 1885 and S. pustulata (Müller, 1786) Ehrenberg, 1838 recognizable in vivo are the shape, the ventral cirral pattern, the caudal cirri, and the mode of moving. The dorsal-bristle complexes are distinguishable by the length of dorsal kinety four and the spaces among the pairs of basal bodies. When the ranges of variation of different populations and clones are compared by biometric analyses, S. vorax shows a relatively stable cortical pattern whereas in S. pustulata the cortical elements are regulated depending on the size of the body and the number of adoral membranelles. In S. vorax morphogenesis begins with a proliferation of basal bodies close to the transverse cirri. In contrast, in S. pustulata, the oral primordium appears de novo between the left marginal row and the postoral cirri. All other morphogenetic events are the same for both species. In proters and opisthes the six anlagen of the frontal-ventral-transverse cirri are of different origin and evolve independently. Three anlagen of the opisthe separate from the oral primordium, two originate from the right, and one from the left postoral cirrus. Three anlagen of the proter evolve from the posteriormost cirrus in the frontal area, one from the parental undulating membranes, one from the buccal cirrus, and one from the cirrus below the buccal cirrus. The anlagen one to six generate one, three, three, three, four, and four cirri. The characteristic arrangement of the undulating membranes and the participation of only two postoral cirri in the formation of primordia provide features that distinguish between the often confused genera Oxytricha and Stylonychia.     

Morphology and morphogenesis of a new marine hypotrichous ciliate (Protozoa,Ciliophora, Pseudoamphisiellidae), including a report on the small subunit rRNA gene sequence

The morphology and morphogenesis of a new marine hypotrichous ciliate Pseudoamphisiella elongata sp. nov. isolated from mussel‐farming waters near Qingdao, China, are described based on living and protargol‐impregnated specimens. Morphologically, the new species can be distinguished from its known congeners by its elongate body shape, narrow oral field, having fewer dorsal kineties and caudal cirri, more marginal cirri, and differentiated pretransverse cirri. The identification as a new species is firmly supported by the sequences of the small subunit ribosomal rRNA (SSU rRNA) gene, compared with other known Pseudoamphisiella species, and the phylogenetic analysis. The morphogenetic characteristics can be summarized as follows: (1) the parental adoral zone of membranelles and undulating membranes are entirely rebuilt by the oral primordium, which develops de novo in the outermost region of the cortex; (2) the oral primordium in the opisthe and the frontoventral–transverse (FVT) anlagen in both dividers are formed independently on the cell surface; (3) an ‘extra’ marginal anlage originates to the right of the right marginal anlage, and develops into two or three ‘extra’ marginal cirri; (4) the FVT anlagen develop in the primary mode, and the last FVT streak contributes two migratory cirri (frontoterminal cirri), which are probably resorbed; (5) the right marginal anlagen in both dividers occur close together, independent of the old structure. © 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 158 , 231–243.