Transverse Flagellum Research Articles

Bimodal Cell Size and Fusing Cells Observed in a Clonal Culture of the Ciguatoxin-Producing Benthic Dinoflagellate Gambierdiscus (WC1/1).

Cells in a clonal culture of the WC1/1 strain of Gambierdiscus that produced ciguatoxin and maitotoxin-3 were observed to spontaneously fuse during the light phase of culture growth. Cells in the process of fusion were indistinguishable from other cells under the light microscope, except that at least one (often both) of the fusing cells displayed an extendible, finger-like protrusion (presumed peduncle) arising from near the sulcul region. Fusion started with one of the cells turning 90° to place the planes of the girdles approximately at right angles to each other, and movement of the transverse flagella ceased in both cells, or in the cell seen in girdle (lateral) view. The cell in girdle view appeared to fuse into the theca of the other cell. The cell that had turned 90° often rounded up and become egg shaped (obovoid) during early fusion. Fusion can be quick (<10 min) or can take more than an hour. We saw no evidence of the theca being shed during fusion. Measurement of the dorsoventral and transdiameters revealed a wide range for cell sizes that were distributed as a bimodal population in the clonal culture. This bimodal cell population structure was maintained in clonal cultures reisolated from a small or large cell from the original WC1/1 culture. Cellular production of ciguatoxins by the WC1/1 clone increased during the first two years in culture with a corresponding decrease in production of maitotoxin-3, but this inverse relationship was not maintained over the following ~1.5 years.

Phylogenomics shows unique traits in Noctilucales are derived rather than ancestral.

Dinoflagellates are a diverse protist group possessing many unique traits. These include (but are not limited to) expansive genomes packaged into permanently condensed chromosomes, photosynthetic or cryptic plastids acquired vertically or horizontally in serial endosymbioses, and a ruffle-like transverse flagellum attached along its length to the cell. When reconstructing character evolution, early branching lineages with unusual features that distinguish them from the rest of the group have proven useful for inferring ancestral states. The Noctilucales are one such lineage, possessing relaxed chromosomes in some life stages and a trailing, thread-like transverse flagellum. However, most of the cellular and molecular data for the entire group come from a single cultured species, Noctiluca scintillans, and because its phylogenetic position is unresolved it remains unclear if these traits are ancestral or derived. Here, we use single cell transcriptomics to characterize three diverse Noctilucales genera: Spatulodinium, Kofoidinium, and a new lineage, Fabadinium gen. nov. We also provide transcriptomes for undescribed species in Amphidinium and Abediniales, critical taxa for clarifying the phylogenetic position of Noctilucales. Phylogenomic analyses suggests that the Noctilucales are sister to Amphidinium rather than an independent branch outside the core dinoflagellates. This topology is consistent with observations of shared characteristics between some members of Noctilucales and Amphidinium and provides the most compelling evidence to date that the unusual traits within this group are derived rather than ancestral. We also confirm that Spatulodinium plastids are photosynthetic and of ancestral origin, and show that all non-photosynthetic Noctilucales retain plastid genes indicating a cryptic organelle.

Lens eyes in protists.

Eyes are not unique to animals. As described by Nilsson and Marshall, prominent eyes, complete with retina and lens, have unexpectedly evolved in single cell dinoflagellates.

Behavioral and mechanistic characteristics of the predator-prey interaction between the dinoflagellate Dinophysis acuminata and the ciliate Mesodinium rubrum

Predator-prey interactions of planktonic protists are fundamental to plankton dynamics and include prey selection, detection, and capture as well as predator detection and avoidance. Propulsive, morphology-specific behaviors modulate these interactions and therefore bloom dynamics. Here, interactions between the mixotrophic, harmful algal bloom (HAB) dinoflagellate Dinophysis acuminata and its ciliate prey Mesodinium rubrum were investigated through quantitative microvideography using a high-speed microscale imaging system (HSMIS). The dinoflagellate D. acuminata is shown to detect its M. rubrum prey via chemoreception while M. rubrum is alerted to D. acuminata via mechanoreception at much shorter distances (89 ± 39 μm versus 41 ± 32 μm). On detection, D. acuminata approaches M. rubrum with reduced speed. The ciliate M. rubrum responds through escape jumps that are long enough to detach its chemical trail from its surface, thereby disorienting the predator. To prevail, D. acuminata uses capture filaments and/or releases mucus to slow and eventually immobilize M. rubrum cells for easier capture. Mechanistically, results support the notion that the desmokont flagellar arrangement of D. acuminata lends itself to phagotrophy. In particular, the longitudinal flagellum plays a dominant role in generating thrust for the cell to swim forward, while at other times, it beats to supply a tethering or anchoring force to aid the generation of a posteriorly-directed, cone-shaped scanning current by the transverse flagellum. The latter is strategically positioned to generate flow for enhanced chemoreception and hydrodynamic camouflage, such that D. acuminata can detect and stealthily approach resting M. rubrum cells in the water column.

Feeding currents facilitate a mixotrophic way of life.

Mixotrophy is common, if not dominant, among eukaryotic flagellates, and these organisms have to both acquire inorganic nutrients and capture particulate food. Diffusion limitation favors small cell size for nutrient acquisition, whereas large cell size facilitates prey interception because of viscosity, and hence intermediately sized mixotrophic dinoflagellates are simultaneously constrained by diffusion and viscosity. Advection may help relax both constraints. We use high-speed video microscopy to describe prey interception and capture, and micro particle image velocimetry (micro-PIV) to quantify the flow fields produced by free-swimming dinoflagellates. We provide the first complete flow fields of free-swimming interception feeders, and demonstrate the use of feeding currents. These are directed toward the prey capture area, the position varying between the seven dinoflagellate species studied, and we argue that this efficiently allows the grazer to approach small-sized prey despite viscosity. Measured flow fields predict the magnitude of observed clearance rates. The fluid deformation created by swimming dinoflagellates may be detected by evasive prey, but the magnitude of flow deformation in the feeding current varies widely between species and depends on the position of the transverse flagellum. We also use the near-cell flow fields to calculate nutrient transport to swimming cells and find that feeding currents may enhance nutrient uptake by ≈75% compared with that by diffusion alone. We argue that all phagotrophic microorganisms must have developed adaptations to counter viscosity in order to allow prey interception, and conclude that the flow fields created by the beating flagella in dinoflagellates are key to the success of these mixotrophic organisms.

Computing Flows Around Microorganisms: Slender-Body Theory and Beyond

We present the mathematical framework that governs the interaction of a forcegenerating microorganism with a surrounding viscous fluid. We review slender-body theories that have been used to study flagellar motility, along with the method of regularized Stokeslets. We investigate the role of a dinoflagellate transverse flagellum as well as the flow structures near a choanoflagellate.

Effect of ambient medium viscosity on the motility and flagella motion of Prorocentrum minimum (Dinophyceae)

The effect of ambient medium viscosity on the motility and flagellar beating motion of the dinoflagellate Prorocentrum minimum was experimentally investigated. Prorocentrum minimum is a thecate desmokont dinoflagellate with two flagella that emerge from the flagellar pore at the anterior end of the cell. A digital holographic particle tracking velocimetry technique was employed to capture the swimming trajectories of hundreds of P. minimum cells and to extract the kinematic motion parameters. The viscosity of the surrounding medium was changed from 1.12 cP (natural sea water at 228C) to 11.31 cP by adding methylcellulose to increase fluid viscosity. In natural sea water, the swimming speeds of P. minimum cells (n 1⁄4 77) in a helical motion ranged from 5.4 to 138.4 mm/s with a mean speed of 51.3+27.9 mm/s. The helix radius and pitch of the swimming trajectories are 3.08+0.64 and 25.34+7.96 mm/s, respectively. The longitudinal flagellum beats with a planar wave at a beating frequency of 87.10+ 10.96 Hz. On the other hand, the transverse flagellum beats with a helical wave at a beating frequency of 45.38+13.61 Hz. As the ambient medium viscosity increases, the beating frequency of flagella decreased and consequently, the swimming speed of P. minimum was reduced.

Description of two species of early branching dinoflagellates, Psammosa pacifica n. g., n. sp. and P. atlantica n. sp.

In alveolate evolution, dinoflagellates have developed many unique features, including the cell that has epicone and hypocone, the undulating transverse flagellum. However, it remains unclear how these features evolved. The early branching dinoflagellates so far investigated such as Hematodinium, Amoebophrya and Oxyrrhis marina differ in many ways from of core dinoflagellates, or dinokaryotes. Except those handful of well studied taxa, the vast majority of early branching dinoflagellates are known only by environmental sequences, and remain enigmatic. In this study we describe two new species of the early branching dinoflagellates, Psammosa pacifica n. g., n. sp. and P. atlantica n. sp. from marine intertidal sandy beach. Molecular phylogeny of the small subunit (SSU) ribosomal RNA and Hsp90 gene places Psammosa spp. as an early branch among the dinoflagellates. Morphologically (1) they lack the typical dinoflagellate epicone–hypocone structure, and (2) undulation in either flagella. Instead they display a mosaïc of dinokaryotes traits, i.e. (3) presence of bi-partite trychocysts; Oxyrrhis marina–like traits, i.e. (4) presence of flagellar hairs, (5) presence of two-dimensional cobweb scales ornamenting both flagella (6) transversal cell division; a trait shared with some syndineansand Parvilucifera spp. i.e. (7) a nucleus with a conspicuous nucleolus and condensed chromatin distributed beneath the nuclear envelope; as well as Perkinsus marinus -like features i.e. (8) separate ventral grooves where flagella emerge and (9) lacking dinoflagellate-type undulating flagellum. Notably Psammosa retains an apical complex structure, which is shared between perkinsids, colpodellids, chromerids and apicomplexans, but is not found in dinokaryotic dinoflagellates.

Moestrupia oblonga gen. & comb. nov. (syn.: Gyrodinium oblongum), a new marine dinoflagellate genus characterized by light and electron microscopy, photosynthetic pigments and LSU rDNA sequence

Hansen G. and Daugbjerg N. 2011. Moestrupia oblonga gen. et comb. nov. (syn.: Gyrodinium oblongum), a new marine dinoflagellate genus characterized by light and electron microscopy, photosynthetic pigments and LSU rDNA sequence. Phycologia 50: 583–599. DOI: 10.2216/11-11.1A small-sized, peridinin-containing, athecate dinoflagellate (13–17 µm long) was isolated into clonal culture from a water sample collected at a nearshore location in Tenerife, Spain (October 2004). Based on phenotypic characters (size, shape, pyrenoid and nucleus position), the culture was identified as Gyrodinium oblongum. However, a detailed ultrastructural examination revealed a number of features that did not fit into the current delineation of the genus Gyrodinium or any other dinoflagellate. Likewise, the molecular phylogeny and sequence divergence estimates based on partial LSU rDNA sequences indicated that this isolate has a taxonomically isolated position, and we therefore propose the new genus Moestrupia to accommodate this species within the Dinophyceae. The ultrastructural study uncovered a number of unique features for Moestrupia, for example, a microtubule supported ventral flange situated along the right cingular border and onto the episome. Also, the exit point of the peduncle, through a lip-like protrusion situated in a cavity on the episome, is new in dinoflagellates. The transverse flagellum appeared less coiled compared to other dinoflagellates, and its distal end terminated some distance within the wide sulcus. The upper cingulum border had a distinct rim supported by microtubules; whereas, the lower cingulum border was indistinct. The apical groove was short and curved and bordered on each side by a delicate rim, which may represent amphiesmal vesicles. It ran from the anterior part of the ventral flange to the middorsal side of the episome. Thus, it differs markedly from that in species of Gyrodinium and emphasizes it being distantly related to this genus.

The action of waving cylindrical rings in a viscous fluid

Dinoflagellates (Pfisteria piscicida) are unicellular micro-organisms that swim due to the action of two eucaryotic flagella: a trailing, longitudinal flagellum that propagates planar waves and a transverse flagellum that propagates helical waves. Motivated by the wish to understand the role of the transverse flagellum in dinoflagellate motility, we study the fundamental fluid dynamics of a waving cylindrical tube wrapped into a closed helix. Given an imposed travelling wave on the structure, we determine that the helical ring propels itself in the direction normal to the plane of the circular axis of the helix. The magnitude of this translational velocity is proportional to the square of the helix amplitude. Additionally, the helical ring exhibits rotational motion tangential to its axis. These calculated swimming velocities are consistent when using the method of regularized Stokeslets with prescribed wave kinematics, regularized Stokeslets with dynamic forcing and Lighthill's slender-body theory, except in cases where the slenderness parameter is not small. The translational velocity results are nearly indistinguishable using the three approaches, leading to the conjecture that the main contribution to this velocity at a cross-section is the far-field flow generated by the portion on the opposite side of the ring. The largest contribution to the rotational velocity at a cross-section comes from the cross-section itself and others nearby, thus the geometric details of the slender body have a larger effect on the results.

Determination of the swimming trajectory and speed of chain-forming dinoflagellate Cochlodinium polykrikoides with digital holographic particle tracking velocimetry

The marine dinoflagellate Cochlodinium polykrikoides is a harmful and highly motile algal species. To distinguish between the motility characteristics of solitary and chain-forming cells, the swimming trajectories and speeds of solitary cells and 2- to 8-cell chains of C. polykrikoides were measured using a digital holographic particle tracking velocimetry (PTV) technique. C. polykrikoides cells exhibited helical swimming trajectories similar to other dinoflagellate species. The swimming speed increased as the number of cells in the chain increased, from an average of 391 μm s−1 (solitary cells) to 856 μm s−1 (8-cell chain). The helix radius R and pitch P also increased as the number of cells in the chain increased. R increased from 9.24 μm (solitary cell) to 20.3 μm (8-cell chain) and P increased from 107 μm (solitary cell) to 164 μm (8-cell chain). The free thrust-generating motion of the transverse flagella and large drag reduction in the chain-forming cells seemed to increase the swimming speed compared to solitary cells. The measured swimming speeds agreed with those from field observations. The superior motility of chain-forming C. polykrikoides cells may be an important factor for its bloom, in addition to the factors reported previously.

Studies on woloszynskioid dinoflagellates III: on the ultrastructure and phylogeny of Borghiella dodgei gen. et sp. nov., a cold-water species from Lake Tovel, N. Italy, and on B. tenuissima comb. nov. (syn. Woloszynskia tenuissima)

Ø. Moestrup, G. Hansen and N. Daugbjerg. 2008. Studies on woloszynskioid dinoflagellates III: on the ultrastructure and phylogeny of Borghiella dodgei gen. et sp. nov., a cold-water species from Lake Tovel, N. Italy, and on B. tenuissima comb. nov. (syn. Woloszynskia tenuissima). Phycologia 47: 54–78. DOI: 10.2216/07-32.1Using ultrastructure and nuclear-encoded large subunit (LSU) rDNA sequences, the woloszynskioid dinoflagellates have been shown recently to form a polyphyletic assemblage. The first group comprises the family Tovelliaceae, with the genera Tovellia and Jadwigia. The present manuscript describes the second group, comprising Borghiella dodgei gen. et sp. nov. from the Italian Alps. The new genus differs in a number of ultrastructural features, of which the most important are the structure of the eyespot (type B sensu Moestrup & Daugbjerg) and the structure of the apical part of the cell. The resting cyst is smooth, in contrast to the cysts of other woloszynskioids such as Tovellia and some species of Woloszynskia. The new species has been previously confused with Tovellia sanguinea, which was responsible for colouring the water of Lake Tovel, in the Italian Alps, blood-red up to 1964. However, B. dodgei may form brown, never truly red blooms as in the case of T. sanguinea. The transverse flagellum of Borghiella carries, in addition to thin hairs found also in other dinoflagellates, a row of shorter, thicker hairs resembling the curly hairs on the homologous, anterior flagellum of the perkinsid Parvilucifera but apparently not observed in any other dinoflagellates. Woloszynskia tenuissima, a well-known cold-water dinoflagellate, has been re-examined using material isolated from Greenland. Based on partial LSU rDNA sequencing it is shown to be related to B. dodgei (sequence divergence only 1.1%) and is transferred to this genus as B. tenuissima comb. nov. We agree with the observations of von Stosch that the cysts of this species are spherical and smooth, in contrast to what was mentioned in the original description by Wołoszyńska.

Ultrastructure of a novel tube-forming, intracellular parasite of dinoflagellates: Parvilucifera prorocentri sp. nov. (Alveolata, Myzozoa)

We have characterized the intracellular development and ultrastructure of a novel parasite that infected the marine benthic dinoflagellate Prorocentrum fukuyoi. The parasite possessed a combination of features described for perkinsids and syndineans, and also possessed novel characters associated with its parasitic life cycle. Reniform zoospores, about 4 μm long, possessed a transverse flagellum, alveoli, a refractile body, a mitochondrion with tubular cristae, a syndinean-like nucleus with condensed chromatin, micronemes, bipartite trichocysts with square profiles (absent in perkinsids) and oblong microbodies. Like Parvilucifera, the zoospores also possessed a shorter posterior flagellum, a heteromorphic pair of central microtubules in the anterior axoneme and a reduced pseudoconoid positioned directly above an orthogonal pair of basal bodies. Early developmental stages consisted of a sporangium about 5–15 μm in diam that contained spherical bodies and amorphous spaces. The undifferentiated sporangium increased to about 20–25 μm in diam before being enveloped by a wall with a convoluted mid-layer. The sporangium differentiated into an unordered mass of zoospores that escaped from the cyst through a pronounced germ tube about 4–5 μm in diam and 10–15 μm long. Weakly developed germ tubes have been described in Perkinsus but are absent altogether in Parvilucifera and syndineans. Comparison of these data with other myzozoans led us to classify the parasite as Parvilucifera prorocentri sp. nov., Myzozoa. Although we were hesitant to erect a new genus name in the absence of molecular sequence data, our ultrastructural data strongly indicated that this parasite is most closely related to perkinsids and syndineans, and represents an intriguing candidate for the cellular identity of a major subclade of Group I alveolates.

ULTRASTRUCTURE AND LSU RDNA‐BASED PHYLOGENY OF ESOPTRODINIUM GEMMA (DINOPHYCEAE), WITH NOTES ON FEEDING BEHAVIOR AND THE DESCRIPTION OF THE FLAGELLAR BASE AREA OF A PLANOZYGOTE1

A small, freshwater dinoflagellate with an incomplete cingulum, identified as Esoptrodinium gemma Javornický (=Bernardinium bernardinense sensu auctt. non sensu Chodat), was maintained in mixed culture and examined using light and serial section TEM. Vegetative flagellate cells, large cells with two longitudinal flagella (planozygotes), and cysts were examined. The cells displayed a red eyespot near the base of the longitudinal flagellum, made of two or three layers of pigment globules not bounded by a membrane. Yellow‐green, band‐shaped chloroplasts, bounded by three membranes and containing lamella with three thylakoids, were present in both flagellate cells and cysts. Most cells had food vacuoles, containing phagotrophically ingested chlamydomonads or chlorelloid green algae; ingestion occurred through the ventral area, involving a thin pseudopod apparently driven by the peduncle. The pusule was tubular, with numerous diverticula in its distal portion, and opened into the longitudinal flagellar canal. Three roots were associated with each pair of flagellar bases, both in vegetative cells and in a planozygote. The longitudinal microtubular root bifurcated around the longitudinal basal body. The planozygote contained a single peduncle and associated structures, and a single transverse flagellar canal with the two converging transverse flagella. Using two ciliates as outgroup species, phylogenetic analyses based on maximum parsimony, neighbor‐joining and posterior probability (Bayesian analysis) supported a clade comprising Esoptrodinium, Tovellia, and Jadwigia.

REPRODUCTION AND SEXUALITY IN PFIESTERIA SHUMWAYAE (DINOPHYCEAE)1

Pfiesteria shumwayae is a heterotrophic dinoflagellate with a widespread distribution in temperate‐subtropical estuarine waters. In this study, five clonal isolates from the eastern coast of North America, one from New Zealand, and a mixed composite of clones were cultured in aquaria and fed live fish. Division, sexuality, and phagotrophic feeding on fish were studied by LM, SEM, and flow cytometry. The development of reproductive cysts isolated from aquaria was followed. Synchronously excysted flagellate populations were examined for sexuality and then for feeding behavior and reproduction when given larval fish. Reproductive cysts varied in size and underwent protoplast division(s), most commonly producing two to eight biflagellated offspring. Fusing gametes, resulting planozygotes, and nuclear cyclosis were documented as evidence of sexuality. Gametes emerged from cysts, and fusions were approximately isogamous. Resulting planozygotes had two longitudinal flagella and one transverse flagellum and apparently fed before encysting. Distinct and lengthy chromosome movements (nuclear cyclosis) occurred in presumed zygotic cysts before nuclear division(s). These cysts did not exhibit dormancy in growing cultures and produced two or four biflagellated offspring. Flagellated cells fed on surficial fish tissues and then encysted for reproduction. Stages indicating a completed sexual cycle (fusion, planozygotes, and nuclear cyclosis) were uncommon or absent in clonal cultures but were relatively abundant in the mixed clone culture. Self‐sterility factors apparently influenced sexuality. Starved populations formed quiescent cysts that released swimming cells when food was provided. Pfiesteria shumwayae was similar in reproduction and sexuality to closely related species.

High-speed video observation of swimming behavior and flagellar motility ofProrocentrum minimum (Dinophyceae)

To understand the functions of the longitudinal and transverse flagella of dinoflagellates, the flagellar waveform and frequency of each flagellum were observed by high-speed video-recording. The longitudinal flagellum emerged from the anterior end of the cell and beat with a planar undulating wave whose plane was perpendicular to the valval sutural plane. The transverse flagellum curved around the anterior end of the cell and beat with a helical wave, with different alternating half pitches. The half pitch corresponding to the parts farther from the cellular antero-posterior axis was shorter than that of the parts closer to the axis. This pattern is described by the ratio of the outer-parts half pitch to the pitch of the whole period of the helix and seems to be characteristic of the dinoflagellates' transverse flagellum.

Autecology of the toxic dinoflagellate Alexandrium ostenfeldii: life history and growth at different temperatures and salinities

Batch culture experime nts were conducted with Alexandrium ostenfeldii, a toxic, marine dinoflagellate common in Danish waters. Growth occurred at 11·3–23·7 °C and from 10 to 40 psu.Maximum division rates of more than 0·3 di visions d−1took place at 20 °C and 15–20 psu. Growth phase variations resulted in mean cell sizes from 12 × 103 to 20 × 103 μm3. Variations in cell size were observed at differ ent temperatures and salinities, and mean cell size was closely correlated with division rate for all temperatures investigated (11·3–23·7 °C) and for salinities between 10 and 30 psu. Sexual stages, fusing gametes and planozygotes were observed in nutrient-deficient cultures of A. ostenfeldii from New Zealand, but mixing of two Danish nutrient-deficient, clonal cultures did not result in mating. Sexual fusion did not lead to the formation of resting c ysts, which are presently known only from nature. Temporary cysts were very common in ageing cultures and in unfavourable environmental conditions that did not permit growth. These cysts showed a high degree of morphological variability. When st ained with calcofluor, the cysts revealed a surface pattern. Germination of temporary cysts caused the release of a naked, biflagellate stage. At germination, the transverse flagellum was located outside the cingulum, next to the longitudinal fl agellum. The transverse flagellum became positioned in the cingulum only after the cell was clear of the cyst wall.

Autecology of the toxic dinoflagellate Alexandrium ostenfeldii: life history and growth at different temperatures and salinities

Batch culture experiments were conducted with Alexandrium ostenfeldii, a toxic, marine dinoflagellate common in Danish waters. Growth occurred at 11.3–23.7 °C and from 10 to 40 psu. Maximum division rates of more than 0.3 divisions d−1 took place at 20 °C and 15–20 psu. Growth phase variations resulted in mean cell sizes from 12 × 103 to 20 × 103 μm3. Variations in cell size were observed at different temperatures and salinities, and mean cell size was closely correlated with division rate for all temperatures investigated (11.3–23.7 °C) and for salinities between 10 and 30 psu. Sexual stages, fusing gametes and planozygotes were observed in nutrient-deficient cultures of A. ostenfeldii from New Zealand, but mixing of two Danish nutrient-deficient, clonal cultures did not result in mating. Sexual fusion did not lead to the formation of resting cysts, which are presently known only from nature. Temporary cysts were very common in ageing cultures and in unfavourable environmental conditions that did not permit growth. These cysts showed a high degree of morphological variability. When stained with calcofluor, the cysts revealed a surface pattern. Germination of temporary cysts caused the release of a naked, biflagellate stage. At germination, the transverse flagellum was located outside the cingulum, next to the longitudinal flagellum. The transverse flagellum became positioned in the cingulum only after the cell was clear of the cyst wall.

GENERAL ULTRASTRUCTURE AND FLAGELLAR APPARATUS ARCHITECTURE OF WOLOSZYNSKIA LIMNETICA (DINOPHYCEAE)

ABSTRACT The ultrastructure of Woloszynskia limnetica Bursa was examined using serial thin section electron microscopy. Sections of W. limnetica reveal numerous chloroplast profiles without any obvious pyrenoids. The extensive pusular complex consists of a “smooth” part and a part lined with electron‐dense particles. The nucleus is located in the episome. A stigma (=eyespot) consisting of numerous electron‐dense globules is situated beneath the amphiesmal vesicles of the sulcal groove. The longitudinal microtu‐bular root extends between the stigma and the amphiesma vesicles. Subthecal fibers occur in conjunction with the microtubules and the stigma. Both flagellar exit apertures are encircled by a broad striated collar, each giving rise to a fiber that extends along the pusular canal opening. The striated collars are interconnected by the ventral ridge fiber. The basal part of the transverse flagellum has, in addition to the normal paraxonemal rod (=striated strand or fiber), a semicircular structure consisting of fibrils. The flagellar apparatus is complex but possesses components typically found in the Dinophyceae. The longitudinal mi‐crotubular root is broad and is connected to both striated collars. The transverse basal body gives rise to the transverse microtubular root, which in turn is associated with microtubules that extend to the interior of the cell and with the transverse striated root. The transitional region of both basal bodies possesses a distinctive fibrous ring attached to each microtubular triplet by short fibers that collectively appear as spokes of a wheel. Not unexpectedly, the flagellar apparatus of Woloszynskia limnetica is much like that of the related Woloszynskia sp.; however, some dif ferences were discovered. A phylogenetic relationship between Woloszynskia limnetica, W. coronata (Wolosz.) Thompson, and W. sp. is indicated based on similarities in pusule and stigma structure.

Ultrastructure of the flagellar apparatus of Noctiluca miliaris Suriray swarmers (Dinophyceae)

The swarmers of Noctiluca miliaris Suriray are not uniflagellate, as was assumed for more than a century, but are biflagellate cells. Their flagellar apparatus displays two distinctly heteromorphic flagella: a long flagellum extending posteriorly (=longitudinal flagellum) and a very short flagellum oriented to the cell's left side (= transverse flagellum). The transverse flagellum is situated in a groove and is therefore not visible in the light microscope. A serial section analysis of the basal apparatus of the swarmers reveals structures which are typical for dinoflagellates including a posteriorly directed micro-tubular root (pmr) and a ventral ridge with microtubular and fibrous components (vrm and vrf). Striated fibrous roots are, however, lacking. The structurally relatively simple flagellar apparatus of N. miliaris swarmers may reflect their functional specialization as (micro-)gametes.