Short Flagellum Research Articles

Culture of the cladoceran Moina macrocopa: Mortality associated with flagellate infection

Cladocerans are important food animals in aquaculture, key grazers in freshwater ecosystems, and model animals for ecotoxicological investigations. Their epibiont community, extensively studied in Daphnia, includes filamentous bacteria, fungi, algae, peritrich ciliates, and rotifers; although epibionts are usually benign, heavy infections can be detrimental. During our laboratory culture of female Moina macrocopa Straus, we observed a novel flagellate infection associated with mortality. At day 10, all M. macrocopa were alive in uninfected cultures, whereas in untreated infected cultures, the survival was significantly lower: only 26% of cladocerans were alive. In infected cultures treated with humic substances (as 25mgL−1 dissolved organic carbon), mortalities were comparable to those in the untreated infected cultures; in contrast, in the infected cultures treated with 4gL−1 sea salt, mortalities were arrested, and 76% of the M. macrocopa were alive at day 10. Moribund cladocerans were transparent, had empty digestive tracts, and greatly reduced motor activity. Free-swimming flagellates moved forward with a wobbling motion, rotating around their long axis; they also attached to cladoceran tissue, the Petri dish, and the glass slide, by the tip of their posterior flagellum. Flagellates preserved for scanning electron microscopy were 6.9±0.7μm long and 2.1±0.3μm wide, with a short anterior flagellum (6.8±1.1μm) and long posterior flagellum (14.1±1.5μm). Multi-functionality of a flagellum, for locomotion and adhesion, is relatively rare, and previously reported from genera within the Kinetoplastea, suggesting that the flagellate on M. macrocopa may belong to this group. To combat flagellate mass occurrence in Moina cultures, we recommend a treatment with 4gL−1 sea salt.

Assembly of the Leishmania amazonensis flagellum during cell differentiation

The flagellar cytoskeleton of Leishmania promastigotes contains the canonical 9+2 microtubular axoneme and a filamentous structure, the paraflagellar rod (PFR), which is present alongside the axoneme. In contrast to promastigotes, which contain a long and motile flagellum, the amastigote form of Leishmania displays a short flagellum without a PFR that is limited to the flagellar pocket domain. Here, we investigated the biogenesis of the Leishmania flagellum at 0, 4, 6 and 24h of differentiation. Light and electron microscopy observations of the early stages of L. amazonensis differentiation showed that the intermediate forms presented a short and wider flagellum that did not contain a PFR and presented reduced motion. 3D-reconstruction analysis of electron tomograms revealed the presence of vesicles and electron-dense aggregates at the tip of the short flagellum. In the course of differentiation, cells were able to adhere and proliferate with a doubling time of about 6h. The new flagellum emerged from the flagellar pocket around 4h after initiation of cell cycle. Close contact between the flagellar membrane and the flagellar pocket membrane was evident in the intermediate forms. At a later stage of differentiation, intermediate cells exhibited a longer flagellum (shorter than in promastigotes) that contained a PFR and electron dense aggregates in the flagellar matrix. In some cells, PFR profiles were observed inside the flagellar pocket. Taken together, these data contribute to the understanding of flagellum biogenesis and organisation during L. amazonensis differentiation.

Ultrastructural studies of spermatogenesis and the functions of Leydig cells and Sertoli cells associated with spermatogenesis in Larimichthys polyactis (Teleostei, Perciformes, Sciaenidae)

Ultrastructural studies of spermatogenesis and the functions of Leydig cells and Sertoli cells were investigated by electron microscope observation. Ultrastructural characteristics of spermatozoa of Larimichthys polyactis (Sciaenidae) have a round head, a nucleus containing highly compact filamentous clusters of chromatin, slightly eccentric nuclear fossa, no acrosome, a short midpiece with a short cytoplasmic channel, and a flagellum showing the classic axoneme structure (9 + 2) and short irregular flagellum lateral fins. The spermatozoon of this species (Sciaenidae) is Perciformes type II: the flagellar axis is parallel to the nucleus, the centriolar complex is outside the nuclear fossa, the proximal centriole is anterior and perpendicular to the distal centriole, and no more than five spherical mitochondria are observed. Each of the well-developed Leydig cells observed during the periods of active meiotic division and before spermiation contains an ovoid vesicular nucleus; a number of smooth endoplasmic reticulum, tubular, or vesicular mitochondrial cristae; and several lipid droplets within the cytoplasm. This indicates that Leydig cells, as typical steroidogenic cells showing several cytoplasmic characteristics, are involved in male steroidogenesis. However, no clear evidence of steroidogenesis or of any transfer of nutrients from the cells to spermatids that appears to be associated with phagocytic function in the seminiferous lobule was observed for Sertoli cells. These findings indicate that Sertoli cells of this species function in phagocytosis and the resorption of products originating from degenerating spermatids and spermatozoa following spermiation.

RELATIONSHIPS BETWEEN SPERM LENGTH AND SPEED DIFFER AMONG THREE INTERNALLY AND THREE EXTERNALLY FERTILIZING SPECIES

It is often assumed that longer sperm, by virtue of their increased swimming speed, have a fertilization advantage over shorter sperm when in competition to fertilize eggs. However, there is surprisingly little evidence for a positive correlation between sperm length and speed. Here we use an approach that accounts for within-male variation in sperm traits to examine the relationships between sperm length and sperm speed across a broad range of species, including three internally fertilizing species and three externally fertilizing species. Our results reveal that correlations between sperm size and speed are indeed present and possibly more common than currently thought. However, the direction of the correlations between sperm length and speed, which are more prevalent within a male's ejaculate than among males, were influenced by fertilization mode in contrasting and unexpected ways. Broadly, the patterns revealed that in externally fertilizing species sperm with longer flagellum and shorter heads relative to their flagellum swam faster, whereas in internally fertilizing species sperm with shorter flagellum and longer heads relative to their flagellum swam faster. We discuss these results in light of sperm competition theory and contrast the intraspecific patterns observed in this study with macroevolutionary patterns of sperm evolution reported elsewhere.

Activation loop phosphorylation of a protein kinase is a molecular marker of organelle size that dynamically reports flagellar length

Specification of organelle size is crucial for cell function, yet we know little about the molecular mechanisms that report and regulate organelle growth and steady-state dimensions. The biflagellated green alga Chlamydomonas requires continuous-length feedback to integrate the multiple events that support flagellar assembly and disassembly and at the same time maintain the sensory and motility functions of the organelle. Although several length mutants have been characterized, the requisite molecular reporter of length has not been identified. Previously, we showed that depletion of Chlamydomonas aurora-like protein kinase CALK inhibited flagellar disassembly and that a gel-shift-associated phosphorylation of CALK marked half-length flagella during flagellar assembly. Here, we show that phosphorylation of CALK on T193, a consensus phosphorylation site on the activation loop required for kinase activity, is distinct from the gel-shift-associated phosphorylation and is triggered when flagellar shortening is induced, thereby implicating CALK protein kinase activity in the shortening arm of length control. Moreover, CALK phosphorylation on T193 is dynamically related to flagellar length. It is reduced in cells with short flagella, elevated in the long flagella mutant, lf4, and dynamically tracks length during both flagellar assembly and flagellar disassembly in WT, but not in lf4. Thus, phosphorylation of CALK in its activation loop is implicated in the disassembly arm of a length feedback mechanism and is a continuous and dynamic molecular marker of flagellar length during both assembly and disassembly.

Sperm morphology, motility, and velocity in naturally occurring polyploid European weatherfish (Misgurnus fossilis L.)

Spontaneous polyploidy has been frequently documented in various fish species. This process may lead to disruption in testicular development and function. In the present study, sperm morphology and motility, elements critical to male fertility, were characterized in the naturally occurring triploid (3n) and tetraploid (4n) European weatherfish, Misgurnus fossilis L. (Teleostei, Cobitidae) inhabiting the upper reaches of the Lužnice River in the Czech Republic. Sperm with smaller heads, shorter flagella, and a lower number of mitochondria was observed in 3n specimens compared with 4n, but no differences were observed in size of midpiece or ultrastructure of sperm. Similar to most teleosts, the European weatherfish spermatozoon lacked an acrosome and consisted of a head (containing DNA), a midpiece (containing mitochondria and proximal and distal centrioles), and a flagellum with 9 + 2 microtubular structure. Sperm velocity was significantly lower in individuals with 4n compared with 3n, whereas no difference in sperm motility was observed. The stepwise linear regression reported significant negative correlations between sperm velocity and length of sperm head (r = −0.92, P < 0.01). In conclusion, the data reported no effect of polyploidy on sperm ultrastructure and motility in the European weatherfish, although it can affect sperm velocity, possibly through differences in head size and the number of mitochondria, which provide ATP for sperm movement.

Myriocin, a Serine Palmitoyltransferase Inhibitor, Blocks Cytokinesis in Leishmania (Viannia) braziliensis Promastigotes

We studied the effect of myriocin, an inhibitor of serine palmitoyltransferase, on cultured Leishmania (Viannia) braziliensis promastigotes. Myriocin significantly reduced synthesis of inositol phosphorylceramide, the major sphingolipid expressed in promastigotes as characterized by thin layer chromatography and electrospray ionization mass spectrometry. Log-phase promastigotes treated with 1μM myriocin showed a 52% reduction in growth rate and morphological alterations such as more rounded shape and shorter flagellum. Promastigotes treated with myriocin also displayed a variety of aberrant cell phenotypes. The percentage of cells with one nucleus and one kinetoplast (1N1K), following treatment with 1 or 5μM myriocin, decreased from 89% (control value) to 27% or 3%, respectively. The percentage of cells with two nuclei (2N2K) varied from 7% (control value) to 19% and 6% for 1 or 5μM myriocin-treated parasites, respectively. High percentage of myriocin-treated parasites exhibited large atypical cells presenting three or more nucleus (32% and 89% for 1 or 5μM myriocin, respectively). Transmission electron microscopy following treatment with 1μM myriocin showed the presence of 4N parasites possibly as a result of an incomplete cytokinesis. Addition of 3-ketodihidrosphingosine to myriocin-treated promastigotes rescue parasite growth and morphology. Addition of ethanolamine did not rescue the myriocin effect on parasite. Our findings indicate that sphingolipids are essential for the completion of cytokinesis, and may play a major role in cell proliferation in L. (V.) braziliensis, thus, differing from data described for Leishmania major sphingolipid-free mutant, where addition of ethanolamine rescue wild-type parasite characteristics.

A new genus, Denhamiana gen. nov., and two new species of land snail from inland central Queensland (Eupulmonata, Camaenidae)

Denhamiana gen. nov. is established for at least two new species of camaenid land snail from inland mid-eastern Queensland. D. laetifica sp. nov. occurs in an area stretching from just west of Eungella, southward through the Denham Range to Pine Mountain, south-east of Nebo, while D. leichhardti sp. nov. is hitherto known only from the more westerly Carborough Range. A third species Denhamiana sp. nov. ‘Dipperu’ is proposed awaiting more specimens. These camaenids are characterised by a combination of morphological features including a large helicoid shell with bold dark brown spiral bands and dark brown apertural lip, a closed umbilicus and a reproductive system featuring a reduced epiphallus, a short vestigial epiphallic flagellum and a cylindrical, sheathed penis that internally has a penial stimulator and triangular verge. Molecular study of one of the species indicates that the genus is a sister group to Bentosites Iredale, 1933 whose species occur in coastal and sub-coastal rainforests in localities between Ayr and Sarina, mid-eastern Queensland.

The role of G proteins in the control of intraflagellar transport

Intraflagellar transport (IFT) is a mechanism used for formation of cilia and flagella in eukaryotes and little is known about its regulation. We propose that a RAB-like protein termed RABL4 (IFT27), which is associated with IFT complexes could be involved in IFT regulation. Indeed, since small GTPases are known for being key regulators of many trafficking processes. We used different approaches in order to determine the role of RABL4 during flagellum formation in Trypanosoma brucei. First, GFP::RABL4 experiments showed that the protein is localized in the cell body, at the basal body and within the flagellum, like all IFT proteins studied so far in trypanosomes. Bi-directional movement of GFP fusion protein was observed in the flagellum. RABL4 silencing demonstrated an essential role in flagellum assembly and revealed a mixture of phenotypes. Some cells do not assemble a flagellum, whereas others produce short flagella filled with material looking like IFT complexes. The structure of these short flagella is severely affected, with disrupted microtubule doublets, mislocalisation of the central pair and impaired PFR (an extra-axonemal structure) construction. The latter one can be excessively large, with numerous layers that affect the shape of the flagellum membrane. We propose that RABL4 could participate to the loading of flagellar precursors into IFT complexes for transport and we are currently analyzing GDP or GTP locked versions of the protein to challenge this hypothesis.

Dissecting the Sequential Assembly and Localization of Intraflagellar Transport Particle Complex B in Chlamydomonas

Intraflagellar transport (IFT), the key mechanism for ciliogenesis, involves large protein particles moving bi-directionally along the entire ciliary length. IFT particles contain two large protein complexes, A and B, which are constructed with proteins in a core and several peripheral proteins. Prior studies have shown that in Chlamydomonas reinhardtii, IFT46, IFT52, and IFT88 directly interact with each other and are in a subcomplex of the IFT B core. However, ift46, bld1, and ift88 mutants differ in phenotype as ift46 mutants are able to form short flagella, while the other two lack flagella completely. In this study, we investigated the functional differences of these individual IFT proteins contributing to complex B assembly, stability, and basal body localization. We found that complex B is completely disrupted in bld1 mutant, indicating an essential role of IFT52 for complex B core assembly. Ift46 mutant cells are capable of assembling a relatively intact complex B, but such complex is highly unstable and prone to degradation. In contrast, in ift88 mutant cells the complex B core still assembles and remains stable, but the peripheral proteins no longer attach to the B core. Moreover, in ift88 mutant cells, while complex A and the anterograde IFT motor FLA10 are localized normally to the transition fibers, complex B proteins instead are accumulated at the proximal ends of the basal bodies. In addition, in bld2 mutant, the IFT complex B proteins still localize to the proximal ends of defective centrioles which completely lack transition fibers. Taken together, these results revealed a step-wise assembly process for complex B, and showed that the complex first localizes to the proximal end of the centrioles and then translocates onto the transition fibers via an IFT88-dependent mechanism.

Comparative Analysis of Movement Characteristics of Lancelet and Fish Spermatozoa Having Different Morphologies

The movement characteristics of the sperm and their flagella obtained from a lancelet and 35 species from almost all orders of fishes were examined using high-speed video microscopy. The aim was to clarify the relationship between the motility parameters of the spermatozoa having different morphologies and how these motility parameters affect the swimming speed of the spermatozoa. The motility parameters representing the flagellar waveform, the wavelength, and the amplitude were neither very different between the spermatozoa of the different species nor related to the swimming speed. In contrast, the beat frequency was remarkably changed in the different spermatozoa and was proportional to the swimming speed. The maximum shear angle of the flagellar wave, which is directly related to the maximum sliding displacement between the doublet microtubules, remained nearly constant while the beat frequency varied widely; therefore, the spermatozoa beat in the constant sliding displacement mode. An analysis of the relationship between swimming speed and flagellar length revealed that short flagella were at a disadvantage in developing swimming speed; however, so were extra-long flagella. The ratio of the swimming speed to the wave velocity calculated from the wavelength and the beat frequency depended on the distance from the glass surface. The swimming speeds calculated using the original resistive-force theory were greater than the measured values. To rationalize the measured values, the ratio between the normal and tangential drag coefficient in the resistive-force theory was corrected; namely, 1.99 at 1 μm and 1.63 at 3 μm from the glass surface.

The cumacean Genus Eudorella (Crustacea: Peracarida) from Japanese Waters, Northwest Pacific, and E. suluensis sp. nov. from the Sulu Sea, Indo-West Pacific

Cumacean crustaceans in the genus Eudorella (Leuconidae) from Japanese waters, in the Northwest Pacific, were examinedand the following 15 species were recognized: E. acuticaudata sp. nov.; E. æquiremis Hansen, 1920; E. bathyalis Vassilenko &amp;Tzareva, 2004; E. bathyhwanghaensis sp. nov.; E. breviflagella sp. nov.; E. dentata Lomakina, 1955; E. emarginata (Kroer,1846); E. fusafusa sp. nov.; E. haradai sp. nov.; E. hwanghaensis Hong &amp; Park, 1999; E. ohtai sp. nov.; E. orientalis sp. nov.;E. parahirsuta sp. nov.; E. ryukyuensis Akiyama &amp; Gamô, 2005; and E. setoensis Akiyama &amp; Gamô, 2006. In addition,Eudorella suluensis sp. nov., was collected from the Sulu Sea, Philippines, Indo-West Pacific, 688–693 m. These speciesinclude 2 groups on the basis of shared morphological characters. Eudorella bathyalis, E. breviflagella sp. nov., E. fusafusa, E.orientalis, and E. setoensis are characterized by a row of simple setae on each side of the carapace, with both E. breviflagellaand E, setoensis also characterized by a short flagellum on antenna 2 in adult males. The other group consists of Eudorellahwanghaensis, E. bathyhwanghaensis, and E. ryukyuensis, from southern Japan, and E. suluensis; with E. hwanghaensis and E. bathyhwanghaensis also characterized by a peculiar secondary sexual character on the tip of the 3rd pereopod in adult males.

Nephroselmis excentrica sp. nov. (Nephroselmidophyceae, Chlorophyta) from Okinawa-jima, Japan

Faria D.G., Kato A. and Suda S. 2012. Nephroselmis excentrica sp. nov. (Nephroselmidophyceae, Chlorophyta) from Okinawa-jima, Japan. Phycologia 50: 271–282. DOI: 10.2216/10-74.1Nephroselmis excentrica Faria et Suda sp. nov. is described on the basis of light and electron microscopy. Phylogenetic analyses based on 18S rDNA sequences of N. excentrica were also conducted. Strains of N. excentrica were isolated from coastal sand samples collected from two localities of Okinawa-jima, Japan. The cells are remarkably right-left flattened and appear eccentrically ovoid or elliptical when viewed from their right or left side. A single, parietal, olive-yellow chloroplast contains one conspicuous large eyespot in its anterior ventral edge near the short flagellum base. The eyespot globules are arranged in two layers. A single conspicuous pyrenoid is surrounded by a single starch sheath, which is dorsally situated. The pyrenoid matrix is traversed by sheet-like thylakoid protuberances. The alga possesses five types of body scales, three types of flagellar scales and two types of hair scales. The cell morphology, pyrenoid structure, scale types and cell size are distinctive from previously described Nephroselmis species, and its eccentric cell shape led us to name this newly proposed species ‘excentrica’. 18S rDNA sequences reveal that N. excentrica forms a monophyletic clade with N. olivacea and N. viridis, but the clade is not supported by high bootstrap values.

퍼킨서스편모충(Perkinsus olseni) 유주자 (Zoospore) 의 미세구조 관찰

Protozoan parasites belonging to the genus Perkinsus elicit severe inflammatory responses and are associated with mass mortality of commercially important marine shellfish worldwide. In the present study, we examined the external features of P. olseni zoospores in detail using light and scanning electron microscopy. Our study showed that the zoospores have an oval body with a long anterior flagellum and a short posterior flagellum. The anterior flagellum has a unilateral array of mastigonemes. Mean body dimensions were 3.37 ± 0.33 μm × 1.72 ± 0.22 μm. The average length of the anterior and posterior flagella was 16.34 ± 1.52 μm and 8.25 ± 1.39 μm, respectively. Zoospores of P. olseni found in Korean waters have shorter and narrower bodies, longer anterior flagella, and shorter posterior flagella than zoospores of Perkinsus spp. found in the mollusks of North America and Europe.

A dysflagellar mutant of Leishmania (Viannia) braziliensis isolated from a cutaneous leishmaniasis patient

BackgroundParasites of the Leishmania genus alternate between the flagellated extracellular promastigote stage and intracellular amastigotes. Here we report the characterization of a Leishmania isolate, obtained from a cutaneous leishmaniasis patient, which presents peculiar morphological features.MethodsThe parasite was cultured in vitro and characterized morphologically using optical and electron microscopy. Identification was performed based on monoclonal antibodies and internal ribosomal spacer typing. In vitro macrophage cultures, murine experimental models and sand fly infections were used to evaluate infectivity in vitro and in vivo.ResultsThe isolate was identified as Leishmania (Viannia) braziliensis. In the atypical promastigotes grown in culture, a short flagellum surrounded or interrupted by a protuberance of disorganized material was observed. A normal axoneme was present close to the basal body but without elongation much further outside the flagellar pocket. A disorganized swelling at the precocious end of the axoneme coincided with the lack of a paraflagellar rod structure. The isolate was able to infect macrophages in vitro, induce lesions in BALB/c mice and infect Lutzomyia longipalpis.ConclusionsNotwithstanding the lack of an extracellular flagellum, this isolate infects macrophages in vitro and produces lesions when inoculated into mice. Moreover, it is able to colonize phlebotomine sand flies. Considering the importance attributed to the flagellum in the successful infection and survival of Leishmania in the insect midgut and in the invasion of macrophages, these findings may bring new light into the infectious mechanisms of L. (V.) braziliensis.

Maintenance of Sperm Variation in a Highly Promiscuous Wild Bird

Postcopulatory sexual selection is an important force in the evolution of reproductive traits, including sperm morphology. In birds, sperm morphology is known to be highly heritable and largely condition-independent. Theory predicts, and recent comparative work corroborates, that strong selection in such traits reduces intraspecific phenotypic variation. Here we show that some variation can be maintained despite extreme promiscuity, as a result of opposing, copulation-role-specific selection forces. After controlling for known correlates of siring success in the superb fairy-wren (Malurus cyaneus), we found that (a) lifetime extra-pair paternity success was associated with sperm with a shorter flagellum and relatively large head, and (b) males whose sperm had a longer flagellum and a relatively smaller head achieved higher within-pair paternity. In this species extrapair copulations occur in the same morning, but preceding, pair copulations during a female's fertile period, suggesting that shorter and relatively larger-headed sperm are most successful in securing storage (defense), whereas the opposite phenotype might be better at outcompeting stored sperm (offense). Furthermore, since cuckolding ability is a major contributor to differential male reproductive output, stronger selection on defense sperm competition traits might explain the short sperm of malurids relative to other promiscuous passerines.

Ochromonas moestrupii sp. nov. (Chrysophyceae), a new golden flagellate from Australia

Andersen R.A. 2011. Ochromonas moestrupii sp. nov. (Chrysophyceae), a new golden flagellate from Australia. Phycologia 50: 600–607. DOI: 10.2216/11-13.1A new marine species of Ochromonas from Port Philip Bay, Victoria, Australia, was described. Cells were metabolic and various shapes included ovoid, lanceolate, oblong, pyriform, spherical and rarely triangular. Normal cell size ranged from 3 to 6 µm wide and 5 to 9 µm long. The long (hairy or immature) flagellum was 1–3 times longer than the cell body. There was a single chloroplast that contained an inconspicuous pyrenoid. There was no eyespot. Cells frequently contained large numbers of oil droplets as well as one or more chrysolaminarin vacuoles. Cysts were not observed. Cells were both free-swimming and attached to a substrate, often by a cytoplasmic stalk. Free-swimming cells frequently had an irregular posterior end formed by a lobose pseudopod. Vegetative cells were mixotrophic and consumed bacteria by capturing them at the base of the short (mature) flagellum. Cell division was observed in various stages but no complete sequence was observed. Early division was recognized when cells were observed with two pairs of flagella. The flagellar pairs separated, the nucleus divided and the cell elongated. The flagellar pairs moved to the ends of the elongated cell, and various cytoplasmic pseudopods were formed, apparently aiding in the separation of the two daughter cells. The chloroplast divided late during cytokinesis, and in some cases the chloroplast failed to divide, causing one daughter cell to be aplastidic. Flagellar hair ultrastructure revealed the typical tripartite structure as well as numerous fine hairs extended from the tubular shaft. The flagella had a distal transitional helix with six gyres, the pyrenoid was slightly penetrated by a chloroplast membrane and the chloroplast was surrounded by membranes continuous with the outer nuclear membrane. The new alga showed some resemblance to the type species, Ochromonas triangulata.

TAXONOMY AND PHYLOGENY OF NEPHROSELMIS CLAVISTELLA SP. NOV. (NEPHROSELMIDOPHYCEAE, CHLOROPHYTA)(1).

Nephroselmis clavistella D. G. Faria et S. Suda sp. nov. is collected from coastal sand samples from the eastern and western coasts of Okinawa-jima Island, Japan. The description of the cultured strains is based on light and electron microscopic observations. The cultured strains are phylogenetically analyzed based on 18S rDNA sequences. The cells are remarkably right-left flattened and appear round or ellipse when viewed from their right or left side, and are ∼5.0 μm in diameter. The posterior flagellum curved around the cell body at rest. A single, parietal, crescent chloroplast is yellowish green and contains one conspicuous eyespot in its anterior-ventral edge near the short flagellum base. A pyrenoid with one starch sheath is located dorsal of the chloroplast. The cells are divided by transverse binary cell division, as is common in other species of this genus. The cell body is covered with five types of scales, and among them four scale types are similar to Nephroselmis rotunda. The fifth scale type is a distinctive spiny and club-shaped stellate scale with 10 spines, four of the 10 spines extended ∼150 nm and each are slightly curved with a hook at the end, whereas six spines are club-shaped blunt ended. This scale morphology, an important taxonomic characteristic, has never been described before for the genus Nephroselmis. The cell's morphology is distinctive from previously described Nephroselmis species, and its unique scale characteristics led us to name this newly proposed species "clavistella," meaning club star.

The ultrathin structure of amoeboid flagellate Thaumatomastix sp. (Thaumatomonadida (Shirkina) Karpov, 1990)

The ultrathin structure of amoeboid flagellate Thaumatomastix sp. is considered. The cell is surrounded by two-layered triangular scales. They are formed on the surface of mitochondria. Pseudopodia grabbing bacteria run from ventricular furrow, which is armored with two longitudinal bands of microtubules. Heterodynamic flagella run from small flagellar pocket. Long back flagellum has thin mastigonemes. Proximal area of short flagellum is covered with flat oval scales. Transitional flagellant zone has no spiral or other additional elements. Transverse plate is localized above cell surface. Kinetosomes are parallel to each other. Vesicular nucleus and Golgi apparatus have typical structure. Oval mitochondria contain tubular cristae. Within cytoplasm, extrusive organelles (kinetocysts) containing amorphous material and capsule were found. The latter consists of muff and cylinder. Plasmodial and cystic phases of development have not been discovered. Contractile vacuole is absent. The resemblance between Thaumatomastix sp. and other thaumatomonads has been discussed.

Biomimetics and cilia propulsion

Many swimming microorganisms are able to propel themselves by the organized beating motion of numerous short flagella or cilia attached to their body surface. For their small size and the inherently viscous nature of the motion, this mechanism is very effective and they can swim several body lengths per second. The quest has been to see if artificial cilia may be developed and if the strategy of cilia propulsion can be used in microfluidic devices to transport fluids in a localized and controllable manner. Babataheri et al. (J. Fluid Mech., this issue, vol. 678, 2011, pp. 5–13) explore the response of chains of small paramagnetic beads that are elastically bonded together to form artificial cilia. The chain or fleximag is tethered to the surface and driven by external magnetic fields, responding also to both fluid and elastic forces. A key observation from their experiments and model is that for a simple planar-forcing strategy there is a hidden symmetry that limits the net transport of fluid.