Oral Apparatus Research Articles

Protozoan phagotrophy from predators to parasites: An overview of the enigmatic cytostome-cytopharynx complex of Trypanosoma cruzi.

Eating is fundamental and from this basic principle, living organisms have evolved innumerable strategies to capture energy and nutrients from their environment. As part of the world's aquatic ecosystems, the expansive family of heterotrophic protozoans uses self-generated currents to funnel prokaryotic prey into an ancient, yet highly enigmatic, oral apparatus known as the cytostome-cytopharynx complex prior to digestion. Despite its near ubiquitous presence in protozoans, little is known mechanistically about how this feeding organelle functions. Intriguingly, one class of these flagellated phagotrophic predators known as the kinetoplastids gave rise to a lineage of obligate parasitic protozoa, the trypanosomatids, that can infect a wide variety of organisms ranging from plants to humans. One parasitic species of humans, Trypanosoma cruzi, has retained this ancestral organelle much like its free-living relatives and continues to use it as its primary mode of endocytosis. In this review, we will highlight foundational observations made regarding the cytostome-cytopharynx complex and examine some of the most pressing questions regarding the mechanistic basis for its function. We propose that T.cruzi has the potential to serve as an excellent model system to dissect the enigmatic process of protozoal phagotrophy and thus enhance our overall understanding of fundamental eukaryotic biology.

Regeneration in Stentor coeruleus.

We often think about regeneration in terms of replacing missing structures, such as organs or tissues, with new structures generated via cell proliferation and differentiation. But at a smaller scale, single cells, themselves, are capable of regenerating when part of the cell has been removed. A classic model organism that facilitates the study of cellular regeneration in the giant ciliate Stentor coeruleus. These cells, which can grow to more than a millimeter in size, have the ability to survive after extensive wounding of their surface, and are able to regenerate missing structures. Even a small piece of a cell can regenerate a whole cell with normal geometry, in a matter of hours. Such regeneration requires cells to be able to trigger organelle biogenesis in response to loss of structures. But subcellular regeneration also relies on intracellular mechanisms to create and maintain global patterning within the cell. These mechanisms are not understood, but at a conceptual level they involve processes that resemble those seen in animal development and regeneration. Here we discuss single-celled regeneration in Stentor from the viewpoint of standard regeneration paradigms in animals. For example, there is evidence that regeneration of the oral apparatus in Stentor follows a sender-receiver model similar to crustacean eyestalk regeneration. By drawing these analogies, we find that many of the concepts already known from the study of animal-scale regeneration and development can be applied to the study of regeneration at the cellular level, such as the concepts of determination, induction, mosaic vs. regulative development, and epimorphosis vs. morphallaxis. We propose that the similarities may go beyond analogy, and that some aspects of animal development and regeneration may have evolved by exploiting pre-existing subcellular developmental strategies from unicellular ancestors.

Genetic variation and tadpoles of the westernmost Himalayan lazy toad Scutiger occidentalis

While the diversity of Scutiger is high in the central and eastern parts of the Himalaya-Tibet orogen, only a single species, Scutiger occidentalis Dubois, 1978, can be found in the westernmost regions, in Northwest India and Pakistan. Little is known about its genetic variation, ecology, and distribution and far less about its larval morphology. Here, we provide new records, detailed morphological data of tadpoles, and genetic data (mtDNA and nDNA) of the species from two, so far unknown localities in northern Pakistan. Molecular analysis confirmed the taxonomic identity of the tadpoles and indicated shallow intraspecific genetic differentiation. Tadpole characterizations were illustrated by detailed imagery of live and preserved specimens. Measurements and qualitative traits on oral apparatus provide relevant taxonomic characteristics to distinguish the tadpoles of this species from other lazy toads.

Morphological and molecular data on tadpoles of the westernmost Himalayan spiny frog Allopaa hazarensis (Dubois & Khan, 1979).

Little is known about the life history, ecology, and distribution of the genus Allopaa (Dicroglossidae) and far less recent data are available about the larvae of this taxon. Here, we provide data on the larval stage of Allopaa hazarensis (Dubois & Khan, 1979) from northern Pakistan based on the examination of three tadpoles. Specimens were obtained from two sites in Buner, Khyber Pakhtunkhwa province, Pakistan. Morphological and genetic analysis (mtDNA and nDNA) confirmed the identity of the tadpoles as A. hazarensis. Tadpole characterizations were illustrated by detailed imagery. Basic measurements and details on oral apparatus provide relevant taxonomic characteristics to distinguish the tadpoles of this species from other spiny frogs. The illustration and description of the tadpole of A. hazarensis should facilitate the identification of this species in the field.

Microbial dysbiosis: The root cause of periodontal disease.

Graphical abstract: A eubiotic oral microbial community resembles a house of cards in its highly regulated and precise assembly, structural complexity, and co-operativity between the resident members and the oral immuno-inflammatory apparatus. Change in one or more of these organizing principles can result in expansion of selected resident species (pathobiont bloom), loss of key species that regulate nutrient flow in the system (keystone species), or a general increase in diversity because of random changes in species abundances. These events, either in isolation or in combination, cause this house of cards to collapse into a state of dysbiosis.

Diversity and Eco-Evolutionary Associations of Endosymbiotic Astome Ciliates With Their Lumbricid Earthworm Hosts.

Coevolution of endosymbionts with their hosts plays an important role in the processes of speciation and is among the most fascinating topics in evolutionary biology. Astome ciliates represent an interesting model for coevolutionary studies because they are so tightly associated with their host organisms that they completely lost the cell oral apparatus. In the present study, we used five nuclear markers (18S rRNA gene, ITS1–5.8S–ITS2 region, and 28S rRNA gene) and two mitochondrial genes (16S rRNA gene and cytochrome c oxidase subunit I) to explore the diversity of astomes inhabiting the digestive tract of lumbricid earthworms at temperate latitudes in Central Europe and to cast more light on their host specificity and coevolution events that shaped their diversification. The present coevolutionary and phylogenetic interaction-adjusted similarity analyses suggested that almost every host switch leads to speciation and firm association with the new host. Nevertheless, the suggested high structural host specificity of astomes needs to be tested with increased earthworm sampling, as only 52 out of 735 lumbricid earthworms (7.07%) were inhabited by ciliates. On the other hand, the diversification of astomes associated with megascolecid and glossoscolecid earthworms might have been driven by duplication events without host switching.

Analysis of Motility Patterns of Stentor During and After Oral Apparatus Regeneration Using Cell Tracking.

Stentor coeruleus is a well-known model organism for the study of unicellular regeneration. Transcriptomic analysis of individual cells revealed hundreds of genes-many not associated with the oral apparatus (OA)-that are differentially regulated in phases throughout the regeneration process. It was hypothesized that this systemic reorganization and mobilization of cellular resources towards growth of a new OA will lead to observable changes in movement and behavior corresponding in time to the phases of differential gene expression. However, the morphological complexity of S. coeruleus necessitated the development of an assay to capture the statistics and timescale. A custom script was used to track cells in short videos, and statistics were compiled over a large population (N ~100). Upon loss of the OA, S. coeruleus initially loses the ability for directed motion; then starting at ~4 h, it exhibits a significant drop in speed until ~8 h. This assay provides a useful tool for the screening of motility phenotypes and can be adapted for the investigation of other organisms.

Gene coexpression networks reveal molecular interactions underlying cichlid jaw modularity

BackgroundThe oral and pharyngeal jaw of cichlid fishes are a classic example of evolutionary modularity as their functional decoupling boosted trophic diversification and contributed to the success of cichlid adaptive radiations. Most studies until now have focused on the functional, morphological, or genetic aspects of cichlid jaw modularity. Here we extend this concept to include transcriptional modularity by sequencing whole transcriptomes of the two jaws and comparing their gene coexpression networks.ResultsWe show that transcriptional decoupling of gene expression underlies the functional decoupling of cichlid oral and pharyngeal jaw apparatus and the two units are evolving independently in recently diverged cichlid species from Lake Tanganyika. Oral and pharyngeal jaw coexpression networks reflect the common origin of the jaw regulatory program as there is high preservation of gene coexpression modules between the two sets of jaws. However, there is substantial rewiring of genetic architecture within those modules. We define a global jaw coexpression network and highlight jaw-specific and species-specific modules within it. Furthermore, we annotate a comprehensive in silico gene regulatory network linking the Wnt and AHR signalling pathways to jaw morphogenesis and response to environmental cues, respectively. Components of these pathways are significantly differentially expressed between the oral and pharyngeal jaw apparatus.ConclusionThis study describes the concerted expression of many genes in cichlid oral and pharyngeal jaw apparatus at the onset of the independent life of cichlid fishes. Our findings suggest that – on the basis of an ancestral gill arch network—transcriptional rewiring may have driven the modular evolution of the oral and pharyngeal jaws, highlighting the evolutionary significance of gene network reuse. The gene coexpression and in silico regulatory networks presented here are intended as resource for future studies on the genetics of vertebrate jaw morphogenesis and trophic adaptation.

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.

Multi-Analytical Framework to Assess the In Vitro Swallowability of Solid Oral Dosage Forms Targeting Patient Acceptability and Adherence.

A lack of effective intervention in addressing patient non-adherence and the acceptability of solid oral dosage forms combined with the clinical consequences of swallowing problems in an ageing world population highlight the need for developing methods to study the swallowability of tablets. Due to the absence of suitable techniques, this study developed various in vitro analytical tools to assess physical properties governing the swallowing process of tablets by mimicking static and dynamic stages of time-independent oral transitioning events. Non-anatomical models with oral mucosa-mimicking surfaces were developed to assess the swallowability of tablets; an SLA 3D printed in vitro oral apparatus derived the coefficient of sliding friction and a friction sledge for a modified tensometer measured the shear adhesion profile. Film coat hydration and in vitro wettability was evaluated using a high-speed recording camera that provided quantitative measurements of micro-thickness changes, simulating static in vivo tablet–mucosa oral processing stages with artificial saliva. In order to ascertain the discriminatory power and validate the multianalytical framework, a range of commonly available tablet coating solutions and new compositions developed in our lab were comparatively evaluated according to a quantitative swallowability index that describes the mathematical relationship between the critical physical forces governing swallowability. This study showed that the absence of a film coat significantly impeded the ease of tablet gliding properties and formed chalky residues caused by immediate tablet surface erosion. Novel gelatin- and λ-carrageenan-based film coats exhibited an enhanced lubricity, lesser resistance to tangential motion, and reduced stickiness than polyvinyl alcohol (PVA)–PEG graft copolymer, hydroxypropyl methylcellulose (HPMC), and PVA-coated tablets; however, Opadry® EZ possessed the lowest friction–adhesion profile at 1.53 a.u., with the lowest work of adhesion profile at 1.28 J/mm2. For the first time, the in vitro analytical framework in this study provides a fast, cost-effective, and repeatable swallowability ranking method to screen the in vitro swallowability of solid oral medicines in an effort to aid formulators and the pharmaceutical industry to develop easy-to-swallow formulations.

Automated tooth segmentation as an innovative tool to assess 3D-tooth movement and root resorption in rodents

BackgroundOrthodontic root resorptions are frequently investigated in small animals, and micro-computed tomography (μCT) enables volumetric comparison. Despite, due to overlapping histograms from dentine and bone, accurate quantification of root resorption is challenging. The present study aims at (i) validating a novel automated approach for tooth segmentation (ATS), (ii) to indicate that matching of contralateral teeth is eligible to assess orthodontic tooth movement (OTM) and root resorption (RR), (iii) and to apply the novel approach in an animal trial performing orthodontic tooth movement.MethodsThe oral apparatus of three female mice were scanned with a μCT. The first molars of each jaw and animal were segmented using ATS (test) and manually (control), and contralateral volumes were compared. Agreement in root volumes and time efficiency were assessed for method validation. In another n = 14 animals, the left first upper molar was protracted for 11 days at 0.5 N, whereas the contralateral molar served as control. Following ATS, OTM and RR were estimated.ResultsATS was significantly more time efficient compared to the manual approach (81% faster, P < 0.01), accurate (volume differences: − 0.01 ± 0.04 mm3), and contralateral roots had comparable volumes. Protracted molars had significantly lower root volumes (P = 0.03), whereas the amount of OTM failed to reveal linear association with RR (P > 0.05).ConclusionsWithin the limits of the study, it was demonstrated that the combination of ATS and registration of contralateral jaws enables measurements of OTS and associated RR in μCT scans.

Protaspis larva of an aglaspidid-like arthropod from the Ordovician of Siberia and its habitat

A fossil larva lacking segmentation of the calcified carapace, closely resembling the trilobite protaspis, has been found associated with other skeletal elements of an angarocaridid Girardevia species in the mid Darriwilian of central Siberia. The presence of protaspis larvae in the angarocaridids, generally believed to represent a branch of the Aglaspidida, supports their proximity to trilobites and proves a low position on the arthropod phylogenetic tree but does not necessarily contradict the chelicerate affinity. The cephalic appendages of angarocaridids bore massive gnathobases with detachable spines, closely similar to those known in extant xiphosurans and in their probable Cambrian relatives. The stratigraphic succession of the angarocaridids, their phosphatized cuticle pieces being abundant in the Ordovician strata of Siberia, shows a gradual improvement of mechanical resistance of their carapaces, eventually resulting in a honeycomb structure. The associated benthic mollusc assemblage is dominated with the bellerophontids showing high mortality at metamorphosis and only the limpet-like Pterotheca, infaunal bivalves, and scaphopods being able to survive this in a substantial number. This suggests a strong selective pressure from predators equipped with well-skeletonised oral apparatuses able to crush mineralized body covers of their prey. Possibly, these were some of the associated conodonts of appropriate size and co-evolving towards their ability to crush more and more resistant cuticle. Less likely candidates for durophagy are endoceratid or orthoceratid cephalopods. Also the angarocaridids themselves, equipped with robust gnathobases of cephalic appendages, apparently predated on benthic shelly animals.

RNA Interference by Cyanobacterial Feeding Demonstrates the SCSG1 Gene Is Essential for Ciliogenesis during Oral Apparatus Regeneration in Stentor.

In the giant ciliate Stentor coeruleus, oral apparatus (OA) regeneration is an experimentally tractable regeneration paradigm that occurs via a series of morphological steps. OA regeneration is thought to be driven by a complex regulatory system that orchestrates the temporal expression of conserved and specific genes. We previously identified a S. coeruleus-specific gene (named SCSG1) that was significantly upregulated during the ciliogenesis stages of OA regeneration, with an expression peak at the stage of the first OA cilia appearance. We established a novel RNA interference (RNAi) method through cyanobacteria Synechocystis sp. PCC6803 feeding in S. coeruleus. The expression of SCSG1 gene was significantly knocked down by using this method and induced abnormal ciliogenesis of OA regeneration in S. coeruleus, suggesting that SCSG1 is essential for OA regeneration in S. coeruleus. This novel RNAi method by cyanobacterial feeding has potential utility for studying other ciliates.

Ontogeny and Phylogeny of a New Hypotrichous Ciliate (Protista, Ciliophora), Metaurostylopsis alrasheidi n. sp., With Establishment of a New Genus Monourostylopsis n. gen.

In the present study, based on both morphologic and phylogenetic analyses, a new genus, Monourostylopsis n. gen., and new species, Metaurostylopsis alrasheidi n. sp. as well as a new combination, Monourostylopsis antarctica (Jung et al., 2011) n. comb. (original combination: Metaurostylopsis antarcticaJung et al., 2011), are suggested. The new genus is diagnosed mainly by having three or more frontoterminal cirri, a midventral complex with midventral pairs and a single midventral row, one right marginal row and two or more left marginal rows. The new genus can be easily separated from the morphologically similar genera mainly by having single right marginal row (vs. two or more right marginal rows). Based on live observation and protargol staining, the morphology and morphogenesis of a new species, M. alrasheidi n. sp. isolated from China, were investigated. The new species can be characterized by: two types of cortical granules; about 22 adoral membranelles; three or four frontoterminal, four or five transverse cirri; about eight midventral pairs and a midventral row of three or four unpaired midventral cirri; three or four left and right marginal rows. The main morphogenetic features of Metaurostylopsis alrasheidi n. sp. can be summarized as: (1) the entire parental ciliature, including the oral apparatus, is renewed; (2) the oral primordium of the proter probably originates within a pouch; (3) the oral primordium of the opisthe forms de novo on the cell surface; (4) the anlagen of marginal rows and dorsal kineties are formed intrakinetally, and (5) the fusion of macronuclear nodules results in an irregular branched mass prior to karyokinesis. In the phylogenetic trees, all the available Metaurostylopsis sequences cluster together in a clade with full support (ML/BI: 100/1.00) revealing that the genus is monophyletic within the large group of core urostylids.

Development of the lamprey velum and implications for the evolution of the vertebrate jaw.

The vertebrate jaw is thought to have evolved through developmental modification of the mandibular arch. An extant jawless vertebrate, the lamprey, possesses a structure called "velum"-a mandibular arch derivative-in addition to the oral apparatus. This leads us to assess the velum's possible contribution to the evolution of jaws. The velar muscles develop from progenitor cells distinct from those from which the oral muscles develop. In addition, the oral and velar regions originate from the different sub-population of the trigeminal neural crest cells (NCCs): the former region receives NCCs from the midbrain, whereas the latter region receives NCCs from the anterior hindbrain. The expression of patterning genes (eg, DlxA and MsxA) is activated at a later developmental stage in the velum compared to the oral region, and more importantly, in different cells from those in the oral region. The lamprey mandibular arch consists of two developmental units: the anterior oral unit and the posterior velar unit. Because structural elements of the lamprey velum may be homologous to the jaw, the evolution of vertebrate jaws may have occurred by the velum being released from its functional roles in feeding or respiration in jawless vertebrates.

Re-discovery and novel contributions to morphology and multigene phylogeny ofMyxophyllum steenstrupi(Ciliophora: Pleuronematida), an obligate symbiont of terrestrial pulmonates

AbstractMyxophyllum steenstrupi is a symbiotic ciliate living in the body slime and mantle cavity of terrestrial pulmonates (Gastropoda: Pulmonata). In the present study, M. steenstrupi was re-discovered after almost 30 years and characterized using an integrative morpho-molecular approach for the first time. Myxophyllum is distinguished by a broadly ovate, about 140 × 115 μm-sized body, a nuclear apparatus typically composed of seven macronuclear nodules and a single micronucleus, a central contractile vacuole, a shallow oral cavity situated in the posterior body region and dense somatic ciliature with extensive thigmotactic field. According to the present phylogenetic analyses of two mitochondrial and five nuclear markers, M. steenstrupi is classified in the predominantly free-living order Pleuronematida (Oligohymenophorea: Scuticociliatia). This order also encompasses other taxa isolated from molluscs and traditionally classified along with Myxophyllum in the order Thigmotrichida. The proper classifications of Myxophyllum was hampered by the dramatic remodelling of its oral apparatus (reduction of the paroral membrane and adoral organelles, formation of vestibular kineties), a transformation that was likely induced by its firm association with terrestrial gastropods. The present study also documents that various ciliate lineages independently became commensals or parasites of various aquatic and terrestrial molluscs.

The Larva and Advertisement Call of Bokermannohyla ahenea (Anura: Hylidae)

Bokermannohyla ahenea is endemic to the Serra da Bocaina, a portion of the Serra do Mar in the Atlantic Forest of Southeastern Brazil. Little information is currently available about this species. Herein, we describe the larval morphology of B. ahenea, including internal oral features, chondrocranium, and hyobranchial apparatus, along with its advertisement call and natural history notes. This is the first description of the chondrocranium and hyobranchial apparatus for a member of the genus Bokermannohyla. The larval external morphology of B. ahenea is similar to those of other species of the B. circumdata group, but it can be distinguished from those of other species of the genus by its oral apparatus. The advertisement call of B. ahenea is complex with many numbers of notes. Also, spectral and temporal parameters of the advertisement call can be used to distinguish B. ahenea from its congeners.

Does the Gonostomum-patterned oral apparatus in hypotrichia carry a phylogenetic signal? Evidence from morphological and molecular data based on extended taxon sampling using three nuclear genes (Ciliophora, Spirotrichea).

The classification of hypotrichs based on the gonostomatid oral structure is widely accepted, but the phylogenetic signal of this character is unknown. Here, we infer the species phylogeny of those gonostomatids for which molecular data are available, plus 26 new sequences of SSU-rDNA, ITS1-5.8S-ITS2 and LSU-rDNA genes. The results indicate that: (i) the endoral is more phylogenetically informative than the paroral; (ii) the structure of the endoral and the Gonostomum-pattern adoral zone of membranelles are plesiomorphies for the hypotrichs sensu stricto; (iii) the group of species possessing these features is monophyletic in all our phylogenetic analyses, except that for the SSU-rDNA; (iv) Schmidingerotrichidae is monophyletic in all trees, suggesting that it is a well-defined family; (v) the Gonostomatidae is polyphyletic in the SSU-rDNA and ITS1-5.8S-ITS2 trees, with Gonostomum, Cladotricha, Cotterillia, Metagonostomum, Paragonostomum and Wallackia distributed among separate clades, but monophyletic in the LSU-rDNA and concatenated trees; (vi) higher hypotrich taxa such as core urostyloids and core sporadotrichids/stichotrichids might have evolved from species that possessed a gonostomatid oral apparatus.

Biomarkers of the influence of pyrethroids and neonicotinoids on amphibian larvae

Currently, most amphibian populations in the world exist under the influence of numerous stress factors. Among them, the main factors that affect almost all terrestrial animals, namely, the fragmentation of habitats, environmental pollution and anthropic transformation of landscapes. Moreover, those factors are joined by negative causes that affect only amphibians – specific viral and fungal infections: ranaviruses (Ambystoma tigrinum virus (ATV), Bohle iridovirus (BIV), and frog virus 3) (also dangerous for some reptiles) and chytrid fungi (Batrachochytrium dendrobatidis and B. salamandrivorans). All these factors are one of the main reasons for the current global decline of amphibian populations in the world. In today's world, agricultural chemicals are one of the most important in terms of toxicity, environmental emissions and total area of impact. Among them, a significant proportion are formed by synthetic insecticides, which include pyrethroids and neonicotinoids. Pollution by these substances has a negative impact on amphibian populations, despite the relatively short period of their life in the environment. The vast majority of studies on the effects of pyrethroid and neonicotinoid insecticides were made in laboratory experiments with the larval stages of tailless amphibians. Tadpoles are easy to get in sufficient quantities and kept in the laboratory. Cypermethrin reduces the viability of tadpoles and causes precocious metamorphosis of survived larvae. However, in a combination with other pesticides, it delays metamorphosis. In addition, embryos were more resistant to pyrethroids than tadpoles. Pyrethroid pesticides cause spasms indicating adverse neurological effects. Formation of oral apparatus abnormalities in tadpoles, anisochromasia and increasing number of immature erythrocytes are also caused by pyrethroids. Neonicotinoids show similar effects. Under the action of imidacloprid the erythrocytes are also disturbed that is showed up in the DNA damage and micronuclei formation. Neurological disorders are manifested in the ability to perceive or respond to a predator, disorientation, erratic movement and loss of balance. Pyrethroids and neonicotinoids have been shown cause a variety of disorders: increase mortality and reduce survival of tadpoles; have a teratogenic effect and affect the metamorphosis and morphological parameters of amphibians; change many biochemical parameters that characterize the protein metabolism and oxidative stress; have genotoxic effects and affect the state of the nervous system and animal behaviour. Most of these parameters are proposed for use as biomarkers of pesticide intoxication.

Ultrastructural Studies on a Model Tintinnid - Schmidingerella meunieri (Kofoid & Campbell, 1929) Agatha & Strüder-Kypke, 2012 (Ciliophora). II. The Oral Apparatus.

The ultrastructure of the oral apparatus is supposed to be significant for elucidating more recent common ancestry and might thus provide support for particular groupings of oligotrichean ciliates. The transmission electron microscopical study on mainly cryofixed Schmidingerella meunieri specimens provides the first detailed data for tintinnids and Oligotrichea in general. Ten new characters are included into the cladistic analysis. These features together with the very limited body of literature suggest that substantial changes in the oral ultrastructure correlate only with the formation of a circular adoral zone in choreotrichids. Despite homoplasious morphological and ontogenetic adaptations to the planktonic lifestyle in halteriid hypotrichs and oligotrichids, their oral apparatuses generally retain the plesiomorphic ultrastructure of the Perilemmaphora. The highly complex ultrastructure of the adoral zone is thus able to accomplish an extension in the zone's functionality without obvious changes; only the position of the adoral zone at the apical cell portion together with a globular to obconical cell shape are apparently crucial. Merely, minute apomorphies characterise the Oligotrichea and tintinnids, respectively. Tintinnids with derived somatic ciliary patterns possess distinct microtubular bundles connecting the oral apparatus with the myoneme in the peduncle.