Feeding Groove Research Articles

The function of the feeding groove of 'typical excavate' flagellates.

Phagotrophic flagellates are the main consumers of bacteria and picophytoplankton. Despite their ecological significance in the 'microbial loop', many of their predation mechanisms remain unclear. 'Typical excavates' bear a ventral groove, where prey is captured for ingestion. The consequences of feeding through a 'semi-rigid' furrow on the prey size range have not been explored. An unidentified moving element called 'the wave' that sweeps along the bottom of the groove toward the site of phagocytosis has been observed in a few species; its function is unclear. We investigated the presence, behavior, and function of the wave in four species from the three excavate clades (Discoba, Metamonada, and Malawimonadida) and found it present in all studied cases, suggesting the potential homology of this feature across all three groups. The wave displayed a species-specific behavior and was crucial for phagocytosis. The morphology of the feeding groove had an upper-prey size limit for successful prey captures, but smaller particles were not constrained. Additionally, the ingestion efficiencies were species dependent. By jointly studying these feeding traits, we speculate on adaptations to differences in food availability to better understand their ecological functions.

An Algorithm for Starved Lubricated Journal Bearings With Optionally Locked Lube Oil Feed Grooves

Abstract Starved lubrication occurs intentionally or unconsciously in many journal bearing applications. However, the determination of its concrete distribution in a journal bearing is rather complex as the different lube oil feed grooves interact with each other due to their connection by the lubricant flow along the pad surfaces and the periodic geometric property of the entire bearing. A robust numerical procedure to determine the lube oil distribution between the different feed grooves in a starved lubricated fixed-pad journal bearing is presented as an extension to Elrod's cavitation algorithm. The enhanced algorithm partly integrates flow rate boundary conditions into the linear system of equations for the solution of Reynolds equation and the transport equation. A strategy to couple these flow rate boundary conditions with the iterative procedure to determine the binary cavitation index is proposed. In particular, the algorithm enables an appropriate modeling of lube oil grooves with locked oil supply including the consideration of groove-specific dissipation or design features like bleed notches. The novel algorithm is implemented as a submodule of a thermo-elasto-hydrodynamic bearing code and validated with test data for a high-speed two-lobe bearing with embedded arc. Furthermore, a comprehensive parametric study provides an insight on the robustness of the implemented numeric procedure. Results, current limitations, and possible extensions to the algorithm are discussed.

Analysis of the influence of lubricant supply conditions on the pressure distribution in squeeze-film dampers

One of the most common ways to reduce vibration in aircraft engines is the use of damping devices. Squeeze-film dampers are the dampers most widely used in aircraft engine designs. The efficiency of squeeze-film dampers is determined by their damping capacity which depends, among other parameters, on the static pressure of oil supply to the damper. This article proposes a method for calculating the static pressure in the feed groove of a hydrodynamic damper depending on the geometric size of the end gap and the value of the lubricant supply pressure. The parameters influencing the static pressure in the damper end gap are determined. Calculations are performed for different values of a hydrodynamic damper end gap, the number and diameter of the supply ports. All calculations presented in the article were performed for a short squeeze-film damper with end gaps and throttles. For comparison of parameters, the dynamic pressure was also calculated for a long squeeze-film damper. It was shown that the size of the end gap has the strongest impact on the pressure in the groove of a squeeze-film damper. It was also shown that the dynamic pressure in the gap may be significantly higher than the static pressure of supply, and failure of the lubricating film may result. In addition, it was also shown that the size of the damper end clearance affects the lubricant flow through the damper.

Biogeography, autecology, and phylogeny of Percolomonads based on newly described species.

Percolomonads (Heterolobosea) are aquatic heterotrophic flagellates frequently found in saline waters up to hypersaline environments. We isolated and cultivated seven strains of percolomonad flagellates from marine waters and sediments as well as from a hypersaline inland lake in the Atacama Desert. Morphological characterizations, comprising light and scanning electron microscopy, revealed only slight differences between the strains mainly limited to the cell shape, length of flagella, and length of the ventral feeding groove. Phylogenetic analyses of the 18S and 28S rDNA genes showed the formation of three fully supported clades within the Percolomonadida: the Percolomonadidae, the Barbeliidae fam. nov. and the Lulaidae fam. nov. We describe two new families (Barbeliidae fam. nov., Lulaidae fam. nov.), a new genus (Nonamonas gen. nov.), and five new species (Percolomonas adaptabilis sp. nov., Lula levis sp. nov., Barbelia pacifica sp. nov., Nonamonas montiensis gen. et sp. nov., Nonamonas santamariensis gen. et sp. nov.). Salinity experiments showed that P.adaptabilis sp. nov. from the Atlantic was better adapted to high salinities than all other investigated strains. Moreover, comparisons of our cultivation-based approach with environmental sequencing studies showed that P.adaptabilis sp. nov. seems to be globally distributed in marine surface waters while other species seem to be more locally restricted.

Microgroove optimization to improve hydrodynamic bearing performance

Several researches on hydrodynamic bearings has looked for alternatives to increase their performance. Solutions involving modifications in oil feeding grooves and bearing geometry, as well as the development of new concepts are examples of these studies. Among these proposals, surface texturing gained a lot of attention with the promising results achieved. In this context, a new approach is investigated to optimize the hydrodynamic bearing performance, considering microgrooves with different depth distributed on the bearing surface. In this work, metrics that evaluate the bearing performance were chosen, in order to establish objective functions to optimize the bearing surface. The results obtained show that a proper microgrooves distribution can increase the bearing performance, allowing the increase of the load capacity, reduction of the viscous shear force and reduction of the average temperature in the bearing. In order to simplify the results obtained for the optimal surface, artificial filters were applied to provide surfaces with greater ease of manufacture, without compromising the improvements achieved in the optimization process. Based on these results, the proposed approach in this paper showed to be a promising alternative to increase the performance of hydrodynamic bearings.

Effect of EDMed rake face grooves on the chip breaking capability of twist drills during deep hole drilling of Al 6061 aluminum alloy

ABSTRACT Deep hole drilling of ductile materials like Al6061 with conventional twist drills is challenging due to premature tool failure caused by chip clogging. Chip breakers, in the form of grooves of varying angles (0°, 5° & 10°) and depth (0.4 & 0.5 mm), created using EDM on the rake face, are proposed to overcome chip clogging. Tool wear, hole roughness, and diameter deviation were measured and analyzed along with chip morphology study for the six grooved tools and compared with plain drill. The grooved tools were successful in breaking the chips which allows for easy evacuation without any clogging. Grooved drills produced desired spiral chips compared to string chips produced by plain drill thus resulting in lesser tool wear rate. While the grooved tools showed stable but slightly higher roughness values, the conventional tools exhibited a linear increasing trend as the drilling progressed. The machined hole surfaces had defects such as feed marks, pitting, grooves, and burnished surfaces. The grooved tools produced comparatively more diameter deviation probably because the well broken chips entered into the drill land/hole surface space. From the results it is clear that groove angle and depth have significant effect on the drill machinability characteristics.

A Model for Tilting Pad Thrust Bearings Operating With Reduced Flow Rate—Do Benefits Outweigh Risks?

Abstract The literature on tilting pad thrust bearings (TPTB) calls for flow reduction as an effective means to reduce drag power losses as well as oil pumping costs. However, the highest level of flow reduction a bearing can undergo while maintaining reliable operation is a key question that demands comprehensive analysis. This paper implements a model into an existing thermo-elasto-hydrodynamic (TEHD) computational analysis tool to deliver load performance predictions for TPTBs operating with reduced flow rates. For bearings supplied with either a reduced flow or an overflow conditions, a sound model for the flow and thermal energy mixing in a feed groove determines the temperature of the lubricant entering a thrust pad. Under a reduced flow condition, the analysis reduces the effective arc length of a wetted pad until matching the available flow. Predicted discharge flow temperature rise and pad subsurface temperature rise from the present model match measurements in the archival literature for an eight-pad bearing supplied with 150% to 25% of the nominal flow rate, i.e., the minimum flow that fully lubricates the bearing pads. A supply flow above nominal rate increases the bearing drag power because the lubricant enters a pad at a lower temperature, and yet has little effect on a thrust pad peak temperature rise or its minimum film thickness. A reduced flow below nominal produces areas lubricant starvation zones, and thus the minimum film thickness substantially decreases while the film and pad's surface temperature rapidly increase to produce significant thermal crowning of the pad surface. Compared to the bearing lubricated with a nominal rate, a starved flow bearing produces a larger axial stiffness and a lesser damping coefficient. A reduction in drag power with less lubricant supplied brings an immediate energy efficiency improvement to bearing operation. However, sustained long-term operation with overly warm pad temperatures could reduce the reliability of the mechanical element and its ultimate failure.

Diversity and phylogeny of percolomonads based on newly discovered species from hypersaline and marine waters

Percolomonads are common freshwater, marine and hypersaline tetraflagellated organisms. Current phylogenetic analyses of eukaryotes comprise only two species of this underinvestigated family. Here, we studied the morphology, salinity tolerance and 18S rDNA gene-based phylogeny of seven percolomonad cultures. We describe three new genera and five novel species of Percolomonadida based on phylogenetic distances and morphological characteristics: Barbelia atlantica, B. abyssalis, Lula jakobsenorum, Nakurumonas serrata and Percolomonas doradorae.The new species show features typical for percolomonads, one long flagellum for skidding, three shorter flagella of equal length and a ventral feeding groove. The new species comprise organisms living in marine and athalassic hypersaline waters with salinity ranging from 10 to 150 PSU. Based on these novel taxa, the taxonomy and phylogeny of Percolatea was extended and further resolved.

Predatory protists.

The vast majority of eukaryotic life is made up of single cells commonly referred to as protists. In this primer, Leander provides an introduction to predatory protists - cells that eat other cells. This lifestyle, in particular the use of phagocytosis, makes endosymbiosis possible and enabled the evolution of complex cells.

Observations on the oral organelle, cytopharynx, and subpellicular structure of a Dileptus sp.

We used scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to observe the oral organelle, cytopharynx, and subpellicular structure of a Dileptus sp. The main results were as follows: (a) the cytostome was located on the ventral surface of the base of the beak, surrounded by a periportal matrix that integrated 135 microtube bundles. When these microtube bundles contract, radially arranged into a disk, the cytostome was closed. When these microtube bundles were stretch, they fell into the cytostome and opens. The diameter of the cytostome was about 16 μm regardless of its closure or opening, indicating that the contraction or elongation of these microtube bundles did not change the size of the cytostome, which was only related to whether it blocked the cytostome, thus determining the opening and closing of the cytostome. There were many microtube bundles on two sides of the feeding trough, which could widen or narrow the feeding trough and facilitate beak feeding. (b) The cytopharynx was basket-like without a bottom with a diameter of about 6 μm and was woven from two kind fibers about 0.08 and 0.19 μm. (c) There were two types of extrusomes under the pellicle. Using transmission electron microscopy，the Type I extrusomes showed narrow and long egg shape, its cross section was circular which is composed by various electronic density of concentric. Using the scanning electron microscope, they were two slightly thin clavate, the length was about 5 μm, the diameter of the middle section was about 0.75 μm, and the diameter of the two ends was about 0.32 μm, they were distributed abundantly between the microtubule fasciculi which were located on both sides of the gap on the feeding groove. Using transmission electron microscopy, the Type II extrusomes showed egg shape. Using the scanning electron microscopy, they were about 1.6 × 0.8 μm in size, they were distributed abundantly under the body pellicle while rarely the proboscis. In addition, many different of developmental stages two types of extrusomes could be also seen in the cytoplasm. (d) There were very well-developed fibrous systems under the pellicle that were woven from fibers about 0.14 μm in diameter that attached to the pellicle and bound some organelles in the cytoplasm (e.g., mitochondria, extrusomes) and other structures to the cytoplasm and maintained cell morphology. The results of this study not only supplement and enrich the morphological contents of the Dileptus sp., but also provide the basis for the study of the taxonomy of the Dileptus sp. It also provides a new method for researchers to explore the morphology and structure of ciliate cells under the cortex by SEM.

Ophirina amphinema n. gen., n. sp., a New Deeply Branching Discobid with Phylogenetic Affinity to Jakobids

We report a novel nanoflagellate, Ophirina amphinema n. gen. n. sp., isolated from a lagoon of the Solomon Islands. The flagellate displays ‘typical excavate’ morphological characteristics, such as the presence of a ventral feeding groove with vanes on the posterior flagellum. The cell is ca. 4 µm in length, bears two flagella, and has a single mitochondrion with flat to discoid cristae. The flagellate exists in two morphotypes: a suspension-feeder, which bears flagella that are about the length of the cell, and a swimmer, which has longer flagella. In a tree based on the analysis of 156 proteins, Ophirina is sister to jakobids, with moderate bootstrap support. Ophirina has some ultrastructural (e.g. B-fibre associated with the posterior basal body) and mtDNA (e.g. rpoA–D) features in common with jakobids. Yet, other morphological features, including the crista morphology and presence of two flagellar vanes, rather connect Ophirina to non-jakobid or non-discobid excavates. Ophirina amphinema has some unique features, such as an unusual segmented core structure within the basal bodies and a rightward-oriented dorsal fan. Thus, Ophirina represents a new deeply-branching member of Discoba, and its mosaic morphological characteristics may illuminate aspects of the ancestral eukaryotic cellular body plan.

Oil sands process-affected water impairs feeding by Daphnia magna

Growth in extraction of bitumen from oil sands has raised concerns about influences of this industry on surrounding environments. Water clearance rate (a surrogate of feeding rate by Daphnia magna) in water containing D. magna exposed to oil sands process-affected water (OSPW) and its principal components, dissolved component (DC) and suspended particulate matter (SPM), was reduced to 72, 29, and 59% of controls, respectively. This study also examined several possible mechanisms for the observed changes algal cell density (i.e., feeding rate). There was no change in the digestive enzymes trypsin or amylase when D. magna were exposed to DC or SPM; however, exposure to total OSPW reduced trypsin activity. Mandible rolling or post-abdominal rejections, which are indicators of feeding and palatability of food, were not affected by any exposures to OSPW. Beating of thoracic limbs, which provides water flow toward the feeding groove, was reduced by exposure to SPM or total OSPW. Peristaltic activity was reduced by exposure to DC, which then might result in reduced digestion time in D. magna exposed to DC, SPM or whole OSPW. All treatments caused an increase in numbers of intact algae cells in the hindgut and excreted material. These results suggest that both DC and SPM affect feeding of D. magna by impairing actions of the digestive system, but most probably not by reducing rates of ingestion.

Numerical modeling of the flow in the squeeze film dampers with oil feed groove by computational fluid dynamic analysis

Squeeze film dampers are widely applied in high rotating speed machinery to reduce vibration, add damping and increase the stability of the system. The traditional method of squeeze film dampers analysis usually involves a complicated calculation program that is limited to a simplified physical model. In this study, the feasibility of applying commercial code ANSYS-FLUENT to study the characteristics of the squeeze film damper is investigated, where the dynamic mesh method is employed. The Zwart–Gerber–Belamri model is applied to simulate the cavitation phenomenon in squeeze film damper. By numerical simulation, the dynamic pressure distribution and oil film force are obtained and then the damping coefficients are acquired. The effect of the cavitation model on the damping coefficients and inertia coefficients is obtained. The parametric study including the squeeze film damper clearance, length and whirl frequency is carried out. The result indicates that the use of the cavitation model will reduce the amplitude of the dynamic oil film force and the hysteresis phenomenon can be observed. It leaves room for further improvement on this method.

Moramonas marocensis gen. nov., sp. nov.: a jakobid flagellate isolated from desert soil with a bacteria-like, but bloated mitochondrial genome.

A new jakobid genus has been isolated from Moroccan desert soil. The cyst-forming protist Moramonas marocensis gen. nov., sp. nov. has two anteriorly inserted flagella of which one points to the posterior cell pole accompanying the ventral feeding groove and is equipped with a dorsal vane—a feature typical for the Jakobida. It further shows a flagellar root system consisting of singlet microtubular root, left root (R1), right root (R2) and typical fibres associated with R1 and R2. The affiliation of M. marocensis to the Jakobida was confirmed by molecular phylogenetic analyses of the SSU rRNA gene, five nuclear genes and 66 mitochondrial protein-coding genes. The mitochondrial genome has the high number of genes typical for jakobids, and bacterial features, such as the four-subunit RNA polymerase and Shine–Dalgarno sequences upstream of the coding regions of several genes. The M. marocensis mitochondrial genome encodes a similar number of genes as other jakobids, but is unique in its very large genome size (greater than 264 kbp), which is three to four times higher than that of any other jakobid species investigated yet. This increase seems to be due to a massive expansion in non-coding DNA, creating a bloated genome like those of plant mitochondria.

Multigene eukaryote phylogeny reveals the likely protozoan ancestors of opisthokonts (animals, fungi, choanozoans) and Amoebozoa

Animals and fungi independently evolved from the protozoan phylum Choanozoa, these three groups constituting a major branch of the eukaryotic evolutionary tree known as opisthokonts. Opisthokonts and the protozoan phylum Amoebozoa (amoebae plus slime moulds) were previously argued to have evolved independently from the little-studied, largely flagellate, protozoan phylum, Sulcozoa. Sulcozoa are a likely evolutionary link between opisthokonts and the more primitive excavate flagellates that have ventral feeding grooves and the most primitive known mitochondria. To extend earlier sparse evidence for the ancestral (paraphyletic) nature of Sulcozoa, we sequenced transcriptomes from six gliding flagellates (two apusomonads; three planomonads; Mantamonas). Phylogenetic analyses of 173–192 genes and 73–122 eukaryote-wide taxa show Sulcozoa as deeply paraphyletic, confirming that opisthokonts and Amoebozoa independently evolved from sulcozoans by losing their ancestral ventral groove and dorsal pellicle: Apusozoa (apusomonads plus anaerobic breviate amoebae) are robustly sisters to opisthokonts and probably paraphyletic, breviates diverging before apusomonads; Varisulca (planomonads, Mantamonas, and non-gliding flagellate Collodictyon) are sisters to opisthokonts plus Apusozoa and Amoebozoa, and possibly holophyletic; Glissodiscea (planomonads, Mantamonas) may be holophyletic, but Mantamonas sometimes groups with Collodictyon instead. Taxon and gene sampling slightly affects tree topology; for the closest branches in Sulcozoa and opisthokonts, proportionally reducing missing data eliminates conflicts between homogeneous-model maximum-likelihood trees and evolutionarily more realistic site-heterogeneous trees. Sulcozoa, opisthokonts, and Amoebozoa constitute an often-pseudopodial ‘podiate’ clade, one of only three eukaryotic ’supergroups’. Our trees indicate that evolution of sulcozoan dorsal pellicle, ventral pseudopodia, and ciliary gliding (probably simultaneously) generated podiate eukaryotes from Malawimonas-like excavate flagellates.

Force coefficients for a large clearance open ends squeeze film damper with a central feed groove: Experiments and predictions

The paper describes a large load squeeze film damper (SFD) test rig, details measurements of dynamic loads inducing circular orbits conducted on a large clearance (c=0.250mm) open ends centrally grooved SFD, and presents the identified experimental SFD force coefficients for operation at three static eccentricities. The rig has a bearing cartridge supported atop four elastic rods and a stationary journal, 0.127mm in diameter. The damper consists of two parallel film lands, 12.7mm in length, separated by a central groove, 6.35mm 9.5mm in depth. In the journal, three equally spaced holes, 120° apart, supply a light lubricant into the central groove and squeeze film lands. The experimental SFD force coefficients are compared to test results obtained earlier for a damper with the same film land lengths but with a smaller clearance (c=0.140mm) and against predictions obtained from an advanced physical model that accounts for the flow field in the central groove and the interaction with the adjacent film lands. Dynamic pressures in the film lands and in the central groove are (not) surprisingly of the same order of magnitude. The central groove affects the dynamic forced response of the test damper to generate large direct damping coefficients, ~3.5 times those derived from classical lubrication formulas. Experimental added mass coefficients are ~7.4 times the predictive classical values. Predictions from an advanced model correlate well with the test data when using a shallow groove depth. The measurements and analysis advance knowledge on the dynamic forced performance of SFDs, point out to the limited value of simplistic predictive formulas, and validate the accuracy of a modern predictive tool.

Closure to “Discussion on ‘Damping and Inertia Coefficients for Two End Sealed Squeeze Film Dampers With a Central Groove: Measurements and Predictions,’” (2013, ASME Paper No. GT2013-94273).

The authors thank Professor Mihai Arghir for having performed the computational fluid dynamics (CFD) simulations of the flow fields for the two test damper configurations. The predictions demonstrate, as expected, the flow field in the deep feed groove and lubricated through feed holes to be extremely complicated. The brief discussion on the evolution of the flow patterns (vortices) along the various planes of observation is most enlightening.As per the question, “how can the magnitude of the groove effective depth be objectively selected knowing that the flow field is so complex?” the authors concur with Dr. Arghir's judgment, that is, one cannot ascertain the effective groove depth from simple knowledge of fluid mechanics. The effective depth depends not only on the geometry of the groove and adjacent film land but also on the lubricant properties and the operating conditions. That is, as stated in the original development analyses of Refs. [19,20] from the discussion, the effective groove depth is an empirical parameter to be determined from matching experimental results to predictions or extracted from a careful assessment of numerical predictions obtained from complete CFD simulations.An example of the first instance is offered by the current paper where the effective depth is obtained from correlating (only) one experimental parameter, namely a force coefficient, to predictions obtained by continuously varying the groove depth when solving the extended Reynolds equation for a centered journal condition. References [26,27] from the discussion and Ref. [1] offer full details on the matching procedure and note the good agreement of predictions to the experimental results for most off-centered or eccentric journal conditions, small to large orbit radii, and multiple frequencies.Recent CFD research [2,3] demonstrates, as Professor Arghir has done, the complexity of the flow field in even simple squeeze film dampers. Most importantly; however, is for the damper practitioner to realize that classical lubrication theory, which regards a feed groove as a region of stagnant fluid and impervious to the kinematics of journal motion, is plain wrong.The authors express their sincere gratitude to Dr. Arghir. In this time and age where everyone is so busy, having taken the time to understand and to enlighten the work of others is a rarity—a demonstration that someone cares. Discussions to published papers are nowadays an unfortunate anachronism.

Collodictyon--An Ancient Lineage in the Tree of Eukaryotes

The current consensus for the eukaryote tree of life consists of several large assemblages (supergroups) that are hypothesized to describe the existing diversity. Phylogenomic analyses have shed light on the evolutionary relationships within and between supergroups as well as placed newly sequenced enigmatic species close to known lineages. Yet, a few eukaryote species remain of unknown origin and could represent key evolutionary forms for inferring ancient genomic and cellular characteristics of eukaryotes. Here, we investigate the evolutionary origin of the poorly studied protist Collodictyon (subphylum Diphyllatia) by sequencing a cDNA library as well as the 18S and 28S ribosomal DNA (rDNA) genes. Phylogenomic trees inferred from 124 genes placed Collodictyon close to the bifurcation of the “unikont” and “bikont” groups, either alone or as sister to the potentially contentious excavate Malawimonas. Phylogenies based on rDNA genes confirmed that Collodictyon is closely related to another genus, Diphylleia, and revealed a very low diversity in environmental DNA samples. The early and distinct origin of Collodictyon suggests that it constitutes a new lineage in the global eukaryote phylogeny. Collodictyon shares cellular characteristics with Excavata and Amoebozoa, such as ventral feeding groove supported by microtubular structures and the ability to form thin and broad pseudopods. These may therefore be ancient morphological features among eukaryotes. Overall, this shows that Collodictyon is a key lineage to understand early eukaryote evolution.

A Numerical Study of Circumferential Groove Effect on the Thermohydrodynamic Performance of a Journal Bearing

A circumferential feeding groove is frequently used in applications where the applied load has a variable direction such as crankcase bearings and automotive turbocharger bearings. In this work a journal bearing with a circumferential feeding groove in loaded zone has been simulated using Computational Fluid Dynamics (CFD). Navier–Stokes equation has been solved using CFD software FLUENT, heat transfer in bush has been considered and full cavitation model has been used. The agreement observed between theoretical predictions and classics published data is acceptable. The results show that: if viscosity is assumed to be a constant, the bearing carrying capacity will be overvalued. A central circumferential groove in load zone makes the maximum bush temperature be increased and bearing carrying capacity be decreased. The groove divided the oil film into two symmetry parts and decreased the maximum pressure at a given eccentricity ratio.

Tsukubamonas globosa n. gen., n. sp., A Novel Excavate Flagellate Possibly Holding a Key for the Early Evolution in “Discoba”

We report the ultrastructure and phylogenetic position of a free-living heterotrophic flagellate, Tsukubamonas globosa n. gen., n. sp. This flagellate was isolated from a pond in the University of Tsukuba, Japan. Under light microscopy, the spherical vegetative cells were naked and highly vacuolated, and always swam with rotating motion. Electron microscopic observations revealed that T. globosa possessed a ventral feeding groove, which is one of the hallmark characteristics of the supergroup Excavata. The position of T. globosa was unresolved in the small subunit ribosomal RNA phylogeny. On the other hand, a multigene phylogeny using α-tubulin, β-tubulin, actin, heat shock protein 90, and translation elongation factor 2 robustly united T. globosa with members of the "Discoba" clade of Excavata, composed of jakobids, euglenozoans, and heteroloboseans, although the precise position of T. globosa in this clade remained unresolved. Our detailed morphological comparisons elucidated that T. globosa possessed a novel set of morphological features, and could not be classified into any taxa in the Discoba clade. Instead we classified T. globosa into Tsukubamonadidae n. fam. under Tsukubamonadida n. ord.