Smooth Flagellum Research Articles

The nut-and-bolt motion of a bacteriophage sliding along a bacterial flagellum: a complete hydrodynamics model

The ‘nut-and-bolt’ mechanism of a bacteriophage-bacteria flagellum translocation motion is modelled by numerically integrating the 3D Stokes equations using a Finite-Element Method (FEM). Following the works by Katsamba and Lauga (Phys Rev Fluids 4(1): 013101, 2019), two mechanical models of the flagellum-phage complex are considered. In the first model, the phage fiber wraps around the smooth flagellum surface separated by some distance. In the second model, the phage fiber is partly immersed in the flagellum volume via a helical groove imprinted in the flagellum and replicating the fiber shape. In both cases, the results of the Stokes solution for the translocation speed are compared with the Resistive Force Theory (RFT) solutions (obtained in Katsamba and Lauga Phys Rev Fluids 4(1): 013101, 2019) and the asymptotic theory in a limiting case. The previous RFT solutions of the same mechanical models of the flagellum-phage complex showed opposite trends for how the phage translocation speed depends on the phage tail length. The current work uses complete hydrodynamics solutions, which are free from the RFT assumptions to understand the divergence of the two mechanical models of the same biological system. A parametric investigation is performed by changing pertinent geometrical parameters of the flagellum-phage complex and computing the resulting phage translocation speed. The FEM solutions are compared with the RFT results using insights provided from the velocity field visualisation in the fluid domain.

Hydrodynamic interactions are key in thrust-generation of hairy flagella

The flagellum in many predatory flagellates is equipped with rigid hairs, which reverse the direction of thrust to generate a feeding current. We have discovered a novel mechanism for thrust generation with hairy flagella, which is fundamentally different from the slender body theory governing smooth flagella. We show that the thrust is generated at the crests of the flagellar wave, thanks to the key role of hydrodynamic interactions among hairs, effectively functioning like a sheet. The mechanism suggests that the optimal flagellum should be long and curvy, consistent with the diverse designs of hairy flagella observed in nature.

Structure of the flagellar apparatus in the bacteriotrophic flagellate Parabodo nitrophilus Skuja, 1948 (Kinetoplastea Excavata)

The structure of the flagellar apparatus in the excavate flagellate Parabodo nitrophilus Skuja has been studied. Two smooth heterodynamic flagella emerge from the bottom of the flagellar apparatus. The kinetosomes connected by their proximal ends lie under an acute angle to each other and bear against the plate on the anteior wall of kinetoplast. The dorsal and ventral rootlets emerge from the kinetosomes and are transformed into dorsal and ventral bands. The latter accompanies the posterior flagellum. The MTR band begins inside the wall of the flagellar pocket. The upper part of the cytopharynx is armored by MTR and FAS bands, cross-banded fibril and structure, and additional microtubules. The MTR band and three additional microtubules surround the bottom part of cytopharynx. The mitochondrium contains compact kinetoplast and discoid cristae. The resemblance of Parabodo nitrophilus with other free-living kinetoplastids is discussed.

Artificial helical microswimmers with mastigoneme-inspired appendages

A smooth flagellum moves in the opposite direction of the propagation of flagellar waves. Conversely, a flagellum covered with appendages perpendicular to the main flagellum, called mastigonemes, moves in the same direction as the propagation of flagellar waves. Inspired by mastigoneme structures in nature, we report the reversal of the swimming direction of magnetically actuated artificial helical microswimmers. The main flagella and mastigonemes of these microswimmers are fabricated together using three-dimensional lithography and electron beam evaporation of ferromagnetic thin films. The results show that the swimming speed and direction can be controlled by changing the length/spacing ratio of the mastigonemes.

Novel Sex Cells and Evidence for Sex Pheromones in Diatoms

BackgroundDiatoms belong to the stramenopiles, one of the largest groups of eukaryotes, which are primarily characterized by a presence of an anterior flagellum with tubular mastigonemes and usually a second, smooth flagellum. Based on cell wall morphology, diatoms have historically been divided into centrics and pennates, of which only the former have flagella and only on the sperm. Molecular phylogenies show the pennates to have evolved from among the centrics. However, the timing of flagellum loss – whether before the evolution of the pennate lineage or after – is unknown, because sexual reproduction has been so little studied in the ‘araphid’ basal pennate lineages, to which Pseudostaurosira belongs.Methods/Principal FindingSexual reproduction of an araphid pennate, Pseudostaurosira trainorii, was studied with light microscopy (including time lapse observations and immunofluorescence staining observed under confocal scanning laser microscopy) and SEM. We show that the species produces motile male gametes. Motility is mostly associated with the extrusion and retrieval of microtubule-based ‘threads’, which are structures hitherto unknown in stramenopiles, their number varying from one to three per cell. We also report experimental evidence for sex pheromones that reciprocally stimulate sexualization of compatible clones and orientate motility of the male gametes after an initial ‘random walk’.Conclusions/SignificanceThe threads superficially resemble flagella, in that both are produced by male gametes and contain microtubules. However, one striking difference is that threads cannot beat or undulate and have no motility of their own, and they do not bear mastigonemes. Threads are sticky and catch and draw objects, including eggs. The motility conferred by the threads is probably crucial for sexual reproduction of P. trainorii, because this diatom is non-motile in its vegetative stage but obligately outbreeding. Our pheromone experiments are the first studies in which gametogenesis has been induced in diatoms by cell-free exudates, opening new possibilities for molecular ‘dissection’ of sexualization.

Increased filtration efficiency of attached compared to free-swimming flagellates

Heterotrophic flagellates often attach to surfaces while feeding. A possible fluid dynamic reason is that attachment increases filtration efficiency. This was investigated experimentally and theoretically. The effect of attachment on flow field and clearance was studied by video microscopy in the nanoflagellates Paraphysomonas vestita and Pteridomonas danica. The flow field around feeding cells was visualised by latex bead suspensions. From a fluid dynamics point of view, it is advantageous to be sessile if the radius of the transectional area of the water flow that is swept for particles is smaller than 1.5 × cell radius. For flagellates with a smooth flagellum, this also requires that the flagellum beats with a large amplitude. For attached P. vestita, clearance is ca. 70% higher relative to free-swimming cells and for P. danica this value is ca. 34%. The difference between the 2 species accords with the fact that Pteridomonas sweeps a wider area of the water flow relative to its cell size than Paraphysomonas. Protozoa may attach for other reasons, such as to remain at sites with high food concentrations, but in the case of suspension feeders, it is also advantageous to attach in terms of fluid dynamics. It is likely that a large proportion of the heterotrophic nanoflagellates in plankton are associated with suspended particles that act as drift anchors, thus enhancing clearance.

Biomineralization Within Vesicles: The Calcite of Coccoliths

Coccolithophores are a group of unicellular plant plankton, which produce exoskeletons of minute calcite plates, called coccoliths. Despite their small size (1–10 μm across), coccoliths are remarkably elaborate biomineral structures characterized by precise control of both nucleation and growth of calcite by the organic system. They are also of considerable environmental and applied geological importance. Coccolithophores occur in enormous abundances, forming a significant proportion of total marine primary production and carbon fixation, especially in open ocean environments. Their biogeochemical impact is magnified by export of coccoliths to the ocean floor, where coccoliths are the largest single component of deep-sea sediments, forming vast accumulations of calcareous oozes and chalks, including the Late Cretaceous chalks of Northwestern Europe. Moreover, coccoliths are extensively employed by geologists as marker fossils to determine the ages of sediments, especially from drill cores. More recently, satellite imaging of immense coccolithophore blooms has led to extensive multi-disciplinary research into their biology and impact on the marine ecosystem and global carbon cycle (e.g., Westbroek et al. 1993; Paasche 2002; Thierstein and Young in press). ### Biological affinities Coccolithophores belong to the algal division (or phylum) Haptophyta. Other haptophytes are non-calcifying and include the well-known genera Phaeocystis, Prymnesium, Pavlova and Chrysochromulina . They are all characterized by possessing golden-brown chloroplasts, two smooth flagella and a third flagellum-like organelle, the haptonema. The haptonema shows distinctive coiling behavior and has a quite different microtubular sub-structure from flagella. Molecular genetic data have shown that the haptophytes are a group discrete from other algal protists that probably originated during the Precambrian (>600 Ma) protist radiation and acquired chloroplasts subsequently (possibly in the Late Palaeozoic, ca. 300–400 Ma) as a result of secondary endosymbiosis (Medlin et al. 1997). Molecular genetic phylogenies of the haptophytes are still being developed, but all results to date (Edvardsen …

The Pinguiophyceae classis nova, a new class of photosynthetic stramenopiles whose members produce large amounts of omega-3 fatty acids

SUMMARY The Pinguiophyceae class. nov., a new class of photo-synthetic stramenopiles (chromophytes), is described. The class includes five monotypic genera, Glossomastix, Phaeomonas, Pinguiochrysis (type genus), Pinguio-coccus and Polypodochrysis. These algae have an unusually high percentage of polyunsaturated fatty acids, especially 20:5 (n-3)(EPA, eicosapentaenoic acid). These fatty acids are the basis for choosing the Latin noun ‘Pingue’ (= fat, grease) as the root for the class name. Analyses of nuclear-encoded 18S rRNA and chloroplast-encoded rbcL gene sequence data showed that these algae formed a monophyletic group that could not be placed in any other class. Morphologically, the species are all single-celled microalgae from picoplanktonic size to over 40 urn in length. Each cell has one (or two) typical chloroplast(s) with a girdle lamella and a surrounding chloroplast endoplasmic reticulum. Pyrenoids occur within the chloroplast, varying from embedded to stalked, and membranes penetrate into the pyrenoid in all five genera. Phaeomonas has motile cells with two flagella, and the forward-directed flagellum bears mastigonemes (tripartite flagellar hairs). Two other genera (Glossomastix, Polypodochrysis) produce zoospores that possess only one smooth flagellum (no mastigonemes), and this flagellum apparently is the mature flagellum, a feature previously unknown in the photosynthetic stramenopiles. The major carotenoid pigments in the pinguiophytes are fucoxanthin, violaxanthin, zeaxanthin and P-carotene, as well as chlorophyll a and chlorophyll c-related pigment(s). These features support recognition of the Pinguiophyceae class. nov. as a unique group of algae.

THE PINGUIOPHYCEAE CLASSIS NOVA, CHROMOPHYTE ALGAE PRODUCING LARGE AMOUNTS OF OMEGA‐3 FATTY ACIDS

A new class of algae is proposed for a small group of unusual chromophytes (=heterokont algae). One novel aspect of these organisms is that cells contain large amounts of polyunsaturated fatty acids (41 – 67% of fatty acids), with exceptionally high amounts of EPA (21 – 56% of fatty acids). A second unusual character is that, for at least two genera, the mature flagellum (short, smooth flagellum of other chromophytes) is dominant, and the immature flagellum (long, hairy flagellum of other chromophytes) lacks tripartite hairs and is reduced in size or even absent. Carotenoid analysis shows that the class is characterized by the presence of chlorophylls a and c, fucoxanthin, violaxanthin, antheraxanthin, zeaxanthin, and β‐carotene. The 18S rRNA and rbcL gene sequences show that these organisms form a monophyletic group that is supported by very high bootstrap values. The phylogenetic relationships of the Pinguiophyceae and other classes are not well resolved, however, the relationships among the chromophytes have always been uncertain. The abundance of EPA, known to reduce “bad cholesterol” in humans, suggests this new class may be of significant economic importance.

Ultrastructure of the colourless flagellate Hyperamoeba flagellata with special reference to the flagellar apparatus

Summary Hyperamoeba flagellata is a fresh-water protist of uncertain taxonomic position. It exists in three living forms: as an amoeba, a flagellate and a cyst. The ultrastructure of the flagellated stage of H. flagellata is investigated here by TEM for the first time. Special attention was paid to the structure of the flagellar apparatus. There is one long smooth flagellum only which is directed anteriorly. It emerges from the flagellar basal body (kinetosome) located at the apical end of the cell. Two cones of microtubules extend from the flagellar base towards the nucleus. The outer cone originates from the lateral side of the flagellar kinetosome, while the inner cone arises from an MTOC associated with the flagellar kinetosome by a short fibrillar rootlet. The second (barren) kinetosome lies ventrally and is directed to the right side of the cell. It has two microtubular rootlets which pass laterally in the same direction. The microtubular cones overlap the anterior end of the nucleus. A dictyosome lies between the basal bodies and the nucleus. Mitochondria with tubular cristae have an electron dense core which is orientated in a longitudinal axis. The structure of the flagellated stage of H. flagellata is compared with flagellated cells of protostelids and cercomonads. It is proposed that this organism may represent a link between protostelids and cercomonads.

Flagella of a chrysophycean alga play an active role in prey capture and selection

The flagella of the pigmented algaEpipyxis pulchra (Chrysophyceae) were observed with image enhanced video microscopy to play an active role in gathering, physically seizing and selecting prey prior to phagocytosis. Vegetative unicells of this sessile, freshwater species possess two structurally and functionally distinct flagella, both active in feeding. During prey gathering the long flagellum, which is adorned with stiff hairs, beats rapidly to direct a strong water current towards the cell while the short, smooth flagellum moves very little. When a potential food particle is drawn by the current to contact the flagellar surfaces, the long flagellum stops beating and positions itself, in concert with the short flagellum, to seize the prey between them. Both flagella then briefly rotate the prey before selecting or rejecting it. If rejected, the particle is discarded by the coordinated activity of both flagella. If selected as food, the prey is held in place until a complex collecting cup emanates out from a position near the basal bodies and engulfs it. The cup plus enclosed food particle, now a food vacuole, is then retracted back to the cell proper.

FINE STRUCTURE OF THE FLAGELLAR APPARATUS OF UROGLENA AMERICANA (CHRYSOPHYCEAE)1

ABSTRACTThe three‐dimensional structure of the flagellar apparatus of Uroglena americana Calkins (Uroglenopsis americana [Calkins] Lemmerman) was determined using serial section reconstruction. The three microtubular rootlet systems (R2, R3, and R4) follow the general pattern found in other chrysophytes. The R2 rootlet originates between the basal bodies of the mastigoneme‐bearing long flagellum (F1) and the short smooth flagellum (F2) and is attached to the former by a fibrous connection. The R3 rootlet system originates as a trough‐shaped band of six microtubules spanning the distance between the proximal ends of the F1 and F2 basal bodies. The six‐membered rootlet splits into two parts (designated R3 and R3) which circle the depression from which the F2 flagellum emerges in counter‐clockwise direction. These two rootlets pass beneath the F2 basal body and descend into the cell alongside the chloroplast. The R4 rootlet originates in fibrous material which passes diagonally over the F2 basal body, forms a clockwise loop about three‐quarters of the way around the depression, and ends in the cytoplasm.In place of a typical chrysophyte R1 rootlet, U. americana has a different array of microtubules attached to the F1 basal body which we have designated the descending rootlet (DR). This rootlet is a hairpin‐shaped structure lying just below the surface of the cell; its longitudinal axis is predominantly parallel to the longitudinal axis of the cell. The DR resembles the bypassing rootlet which occurs in phaeophyte zoospores. Other chrysophytes may possess rootlets which are similar to the DR found in Uroglena.

FINE STRUCTURE OF THE FLAGELLAR APPARATUS OF DINOBRYON CYLINDRICUM (CHRYSOPHYCEAE)1

ABSTRACTThe three‐dimensional structure of the flagellar apparatus of Dinobryon cylindrioum Imhof. (UTEX no. LB 2266) was determined using serial section reconstruction. Four microtubular rootlet systems (R1, R2, R3, and R4)and a rhizoplast are present, following the general pattern found in other chrysophytes. The R1 rootlet, containing seven microtubules, originates at the basal body of the long flagellum that bears mastigonemes (F1). The R1 rootlet forms an arc which curves in clockwise direction (when viewed from the anterior end of the cell) approximately halfway around the pit from which the short smooth flagellum (F2) emerges. Numerous microtubules cascade from the exterior‐facing side of this rootlet to the tail of the cell. The R2 rootlet originates between the F1 and F2 basal bodies, is attached to the F1 basal body by a fibrous connection, and forms a clockwise arc above the R1 rootlet. This rootlet extends approximately one quarter of the way around the pit. The R3 rootlet system originates as a trough‐shaped band of six microtubules spanning the distance between the proximal ends of the F1 and F2 basal bodies. The six‐membered rootlet splits into two parts, designated R3 and R3. Both parts circle the pit in counter‐clockwise direction, pass beneath the F2 basal body, and descend into the cell alongside the chloroplast. The R4 rootlet originates in fibrous material, passes diagonally over the top of the F2 basal body, forms a clockwise loop at least three quarters of the way around the pit to the interior of the R3 and R3 rootlets, and ends in the cytoplasm.Similarities of rootlet origins and other details of the flagellar apparatus of D. cylindricum with those of other heterokont organisms reinforce the idea that these organisms are phylogenetically related.

Flagellar transformation in the heterokontEpipyxis pulchra (Chrysophyceae): Direct observations using image enhanced light microscopy

Cells ofEpipyxis pulchra possess two heteromorphic flagella that differ markedly in function, particularly during motility and prey capture. Flagellar heterogeneity is achieved during the course of at least three cell cycles. Prior to cell division, cells produce two new long, hairy flagella while the parental long flagellum is transformed into a new short, smooth flagellum. The parental short flagellum remains a short flagellum for this and subsequent cell division cycles. Although flagellar transformation requires only two cell cycles, developmental differences exist between daughter cells and the maturation of a flagellum/basal body requires at least three cycles.

Wigwamma scenozonionsp.nov. (Prymnesiophyceae) from West Greenland

Wigwamma scenozonion sp. nov. (Prymnesiophyceae) is described on the basis of electron microscopy of shadowcast whole mounts prepared from water samples collected in the vicinity of Godhavn (West Greenland) in July and August 1977. This nanoplanktonic coccolithophorid possesses two smooth flagella and a shorter coiling haptonema. Coccoliths of one type cover the whole cell. Each coccolith is composed of a ring of rod-like crystallites joined end to end and arranged parallel to the edge of the oval coccolith base-plates. A single enlarged crystallite is found on most coccoliths. W. scenozonion is distinguished from the two previously described Wigwamma species by the lack of coccolith superstructures and by having one, rather than two rings of crystallites along the base-plate edge. In addition to the West Greenland specimens a single W. scenozonion cell has been encountered in a water sample from Denmark.

The structure and phylogenetic significance of the flagellar transition region in the chlorophyll c-containing algae

An electron-dense helix is the most conspicuous structure in the flagellar transition region of members of the algal class Chrysophyceae. This “transitional helix” (TH) lies immediately distal to a partition across the flagellar axoneme which occurs exactly at the level at which the flagellum enters the cell body. The helix surrounds the central axonemal pair and lies at a distance of 10 nm from the 9 peripheral doublets. From the new data presented and a survey of published observations on the structure of the transition region of all the chlorophyll c-containing classes of algae, it is shown that a TH characteristic of the Chrysophyceae, Xanthophyceae and Eustigmatophyceae. The number of TH gyres varies from 3 to 6 in the Xanthophyceae and from 1 to 8 in the Chrysophyceae. In any one species, however, the TH is the same size in both the long flagellum which bears tubular mastigonemes and in the short smooth flagellum, though in some chrysophytes where the short flagellum is vestigial the number is fewer than in the normal flagellum. A TH appears to be absent from the Rhaphidophyceae and zoids of the Bacillariophyceae and Phaeophyceae though the structure of the transition region in these groups otherwise resembles that of the Chrysophyceae, Xanthophyceae and Eustigmatophyceae. The value of transition region variation in determining evolutionary relationships among the chlorophyll c-containing algal classes is assessed against a background of current ideas on their taxonomy and phylogeny. The relevant structural and biochemical features are tabled, and a phylogenetic scheme is presented which appears most logically to interpret these data. It is suggested that the line leading to the Eustigmatophyceae probably diverged from that leading to the strictly heterokont classes Xanthophyceae, Chrysophyceae, Phaeophyceae and Bacillariophyceae before evolution of a girdle lamella in the chloroplast and a photoreceptor apparatus involving a swelling at the proximal end of the short flagellum and an intraplastidial eyespot. The possession of a TH by both the Chrysophyceae and Xanthophyceae adds further support to the concept of their close relationship based on a range of other features. The exceptional absence of a TH from the chrysophycean genera Pedinella and Pseudopedinella reinforces the idea that these taxa are remote from the main chrysophycean line. Absence of a TH from the Phaeophyceae and Bacillariophyceae which otherwise share many important features with the Chrysophyceae and Xanthophyceae is probably a result of loss owing to the functional and morphological specialization of the zoids of these two groups. Transition region structure does not clarify the possible relationships of the Rhaphidophyceae, Prymnesiophyceae, Cryptophyceae or Dinophyceae. The proposed phylogeny supports the idea of a mutually related “heterokont” protist assemblage comprising the Chrysophyceae, Xanthophyceae, Phaeophyceae, Bacillariophyceae and possibly Rhaphidophyceae and the Oomycetes (water moulds) though in the latter the TH is replaced by a dense cylinder with a corrugated wall which may or may not be homologous with it. Structures resembling a TH have been described in a wide variety of other flagellated cells including the prasinophyte Pyraminonas orientalis, one species of the colourless flagellate genus Bicosoeca and the proteromonads Karotomorpha and Proteromonas. Only in the latter genera does homology with a TH seem likely on present evidence, suggesting that flagellates of this type may have evolved from chrysomonad-like ancestors.

The generation of feeding currents by flagellar motions

The use of flagella by sessile organisms to generate feeding currents is analysed. The organism consists of a spherical cell body (radius A) to which a smooth flagellum (radius a, length L) is attached radially. The cell body is a height H above the plane substrate to which it is rigidly attached via a stalk. The organism propagates plane sinusoidal waves (amplitude α, wavenumber k) from base to tip. The flagellum is represented by distributions of stokeslets and dipoles along its centre-line. The cell body and substrate are modelled by employing an approximate form of the Green's function for the sphere in the half space. The error terms in the model are O(a/L) and O(A2/H2). The analysis and method of solution are adapted from Higdon (1979).The mean flow rate and power consumption are calculated for a wide range of parameters. Optimal motions are determined with the criterion of minimizing the power required to achieve a given flow rate. The optimum wave has maximum slope in the range 2 < αk < 2·5 (compared to the optimum value αk = 1 for swimming). The optimum number of waves Nλ increases linearly with flagellar length for L/A > 10 and is approximately constant, Nλ = 1, for shorter flagella. The optimum flagellar length is in the range 5 < L/A < 10. There is no optimum flagellar radius a/A. For optimal efficiency, the height H should be greater than or equal to the length of the flagellum.The optimum values of the parameters are compared to the values for the choano-flagellates described by Lapage (1925) and Sleigh (1964). Excellent agreement is found between the predicted optima and the observed values. The calculated velocity field closely resembles the flow described by Sleigh and Lapage.

Gametogenesis and gamete structure ofEnteromorpha intestinalis(L.) Link

The process of gametogenesis and gamete structure have been studied using scanning and transmission electron microscopy. Rounding off of the protoplast is followed by three mitotic divisions of the nucleus and cytokinesis to give eight gametes in each gametangium. Changes in wall structure of the gametangium and loosening of wall microfibrils takes place at the site of the future exit pore where the outer cell wall is stretched to form a characteristic “papilla”. Anisogametes are shed, each with two smooth flagella, a single nucleus, a very large chloroplast with a conspicuous pyrenoid and an eyespot composed of one layer of osmiophilic granules.

Balaniger balticus gen. et sp.nov. (Prymnesiophyceae) From Danish coastal waters

Balaniger balticus gen. et sp.nov. (Prymnesiophyceae) is described on the basis of electron microscopy of shadow-cast whole mounts, prepared from water samples collected in October 1975 at localities in the western Baltic. The saddle-shaped cell has two smooth flagella and a short haptonema. The cell surface is covered with oval organic scales supporting calcified pyramid-like structures. Confirmation of the calcification of the periplast has been achieved by applying an X-ray analytical electron probe to one of the specimens observed.

Fine structure of photo-kinetic systems inDinobryon cylindricumvar.Alpinum(chrysophyceae)

The ultrastructure of the stigma and associated flagellar-microtubular systems in Dinobryon cylindricum var. alpinum is described in detail and compared with observations on comparable photo-kinetic systems in other chrysophycean organisms. The chloroplastidic stigma of D. cylindricum var. alpinum is shown to lie in a particular positional relationship to the flagellar swelling in the anterior furrow and to several other organelles, to consist of a monolayer of c. 40 pigmented granules, each c. 250–500 nm diameter, arranged in a definite pattern, and to be overlain by several membrane systems. Other cytoplasmic pigmented bodies with dense crystalline contents surrounded by a single “unit membrane” aggregate near the anterior furrow on the side opposite the stigma. The swelling on the proximal portion of the smooth flagellum is separated from the plasmalemma of the anterior furrow by a nearly constant distance of 75–100 nm, has a multilamellate substructure that is linked by fine radiating interconnections to the axoneme doublets, and is connected to the plasmalemma by a system of fibrillar interconnections. A transitional helix in the basal body region is described as similar to structures reported in other chrysophycean flagellates. A striated rhizoplast with a periodicity of c. 90 nm extends from basal body I to the nuclear envelope. A seven-stranded microtubular root extends from the same basal body. Other fibrous and microtubular root systems are also described. The inter-relationships and possible functions of the aforementioned structures are discussed.