A study on the amoebo-flagellate transformation in the slime moldEchinostelium minutum de Bary

Summary The structure and behavior of the non-flagellate and flagellate phases of the slime moldEchinostelium minutum de Bary are here described from living cultures examined with phasecontrast microscopy. The ultrastructure of the myxamoebal and swarm cell phases was studied in sectioned material fixed sequentially with glutaraldehyde-acrolein and OsO₄.The nearly spherical myxamoeba has two pairs of juxtanuclear centrioles with associated microtubular arrays. During the amoebo-flagellate transformation each pair of centrioles assumes an anterior position in the cell and becomes arranged at right angles to one another within a cone of microtubules. This microtubular cytoskeleton extending under the plasmalemma establishes the twisted, narrowly ovoid form of the swarm cell. Each centriole functions potentially as a basal body. When transformed in phosphate buffer pH 6.8 at 12 °C and a cell concentration of 5×10⁵/ml, the myxamoebae develop 1 to 8 flagella. The average number of flagella per swarm cell is 2.7. After approximately 2 hours the swarm cells begin to revert to myxamoebae by resorption of their flagella. The phylogenetic implications of these light and ultrastructural observations are discussed with regard to possible evolutionary relationships between theProtostelia andMyxomycetes.     

Obligate amoebae of the protostelids: significance for the concept of Eumycetozoa

Most flagellate Eumycetozoa have a non-flagellate, or obligately amoeboid, trophic state which differentiates from the amoebo-flagellate state and gives rise to the fruiting body. This study examines the morphology, general ultrastructure, and microtubular systems of the obligate amoebae of three flagellate protostelids with typical amoebo-flagellate states. The obligate amoebae of all three species are morphologically distinct indicating that the obligately amoeboid state has evolved independently in the history of each species. Therefore, obligate amoebae may be useful for defining separate evolutionary groups within the Eumycetozoa.     

RECONSTRUCTION OF THE FEEDING APPARATUS IN PLOEOTIA COSTATA (EUGLENOPHYTA) AND ITS RELATIONSHIP TO OTHER EUGLENOID FEEDING APPARATUSES

The ultrastructure of the feeding apparatus in Ploeotia costata Farmer and Triemer was determined and compared to other euglenoid feeding apparatuses. The feeding apparatus opened subapically onto the ventral surface and extended nearly the entire length of the cell. It consisted of four parts at the anterior surface: a comb, cytostome/pocket, vanes, and supporting rods. The comb was a multilayered structure of three horizontal microtubular rows encased in cement and formed the dorsal lip of the apparatus. The cytostome/pocket was located between the comb and the supporting rods, tapered into the cell as the cytopharynx and was surrounded by five vanes. The electron-opaque vanes extended the entire length of the feeding apparatus and were lined with microtubules for most of their length. Finally, two cement supporting rods that were joined by a crosspiece at the anterior end formed the ventral lip. The rods separated briefly before merging with the vanes. As the merged rods and vanes descended into the cell, they gradually narrowed and terminated. Comparisons of the feeding apparatus with Ploeotia vitrea, Diplonema ambulator, Lentomonas applanatum, and other euglenoids have led to the conclusion that the Type II feeding apparatus is found only in Ploeotia species.     

The flagellar apparatus of the glaucophyte Cyanophora cuspidata

Glaucophytes are a kingdom‐scale lineage of unicellular algae with uniquely underived plastids. The genus Cyanophora is of particular interest because it is the only glaucophyte that is a flagellate throughout its life cycle, making its morphology more directly comparable than other glaucophytes to other eukaryote flagellates. The ultrastructure of Cyanophora has already been studied, primarily in the 1960s and 1970s. However, the usefulness of that work has been undermined by its own limitations, subsequent misinterpretations, and a recent taxonomic revision of the genus. For example, Cyanophora's microtubular roots have been widely reported as cruciate, with rotationally symmetrical wide and thin roots, although the first ultrastructural work described it as having three wide and one narrow root. We examine Cyanophora cuspidata using scanning and transmission electron microscopy, and construct a model of its cytoskeleton using serial‐section TEM. We confirm the earlier model, with asymmetric roots. We describe previously unknown and unsuspected features of its microtubular roots, including (i) a rearrangement of individual microtubules within the posterior right root, (ii) a splitting of the posterior left root into two subroots, and (iii) the convergence and termination of the narrow roots against wider ones in both the anterior and posterior subsystems of the flagellar apparatus. We also describe a large complement of nonmicrotubular components of the cytoskeleton, including a substantial connective between the posterior right root and the anterior basal body. Our work should serve as the starting point for a re‐examination of both internal glaucophyte diversity and morphological evolution in eukaryotes.     

FURTHER STUDIES OF PRESUMEDLY PRIMITIVE GREEN ALGAE,INCLUDING THE DESCRIPTION OF PEDINOPHYCEAE CLASS. NOV. AND RESULTOR GEN. NOV.1

The tiny jumping flagellate originally described as Pedinomonas mikron Throndsen was isolated into pure culture from Australian waters and its ultrastructure critically examined. Pedinomonas mikron differs in behavior and in features of the flagellar apparatus from P. minor, the type species from freshwater, and is referred to the new genus Resultor. The two genera are closely related and form the new class Pedinophyceae, which is characterized by features of the flagellar apparatus, mitosis, and cytokinesis. The flagella show the 11/5 orientation otherwise characteristic of Ulvophyceae and Pleurastrophyceae, but they are arranged end to end as in the Chlorophyceae. The flagellar root system is asymmetric and includes a rhizoplast that emerges from the base of one flagellum but subsequently associates with a microtubular root from the second basal body. Mitosis studied previously by Pickett-Heaps and Ott in Pedinomonas is closed, unlike in other green algae, and the spindle is persistent. No phycoplast or phragmoplast is formed during cytokinesis. The eyespot of the Pedinophyceae is located at the opposite end of the cell from the flagella and adjacent to the pyrenoid, as in the most primitive members of the Prasinophyceae. Members of the Pedinophyceae lack prasinoxanthin and Mg 2,4D, characteristic of certain other primitive green algae. The primitive green algae include the classes Prasinophyceae and Pedinophyceae. Micromonadophyceae Mattox et Stewart is considered a synonym of Prasinophyceae. Two new orders are established, Pedinomonadales, containing all known members of the Pedinophyceae, and Scourfieldiales, with the single family Scourfieldiaceae fam. nov. and the single genus Scourfieldia.     

The ultrastructure of Ancyromonas, a eukaryote without supergroup affinities

The small heterotrophic flagellate Ancyromonas (=Planomonas) lacks close relatives in most molecular phylogenies, and it is suspected that it does not belong to any of the recognized eukaryote 'supergroups', making it an organism of great evolutionary interest. Proposed relatives include apusomonads and excavates, but limited understanding of the ancyromonad cytoskeleton has precluded identification of candidate structural homologies. We present a detailed analysis of the ultrastructure of Ancyromonas through computer-based reconstruction of serial sections. We confirm or extend previous observations of its major organelles (mitochondria, Golgi body, extrusomes, etc.) and pellicle, and distinguish a system of stacked endomembranes that may be developmentally connected to the glycocalyx. Ancyromonas has two basal bodies, each with its own flagellar pocket. The anterior basal body associates with two microtubular elements: a doublet root that runs from between the basal bodies to support the cell's rostrum, and a short singlet root. The posterior basal body is associated with two multi-microtubular structures and a singlet root. One multi-microtubular structure, L1, is a conventional microtubular root. The other structure appears as a curved ribbon of ～8 microtubules near the basal body, but then flares out into two multi-microtubular elements, L2 and L3, plus two single microtubules. The posterior singlet root originates independently near this second complex. L1, the singlet, L2, and L3 all support the posterior flagellar pocket and channel. We also identified several groups of peripheral microtubules. Possible homologies with the flagellar apparatus of both apusomonads and excavates include a splitting root on the right side of the posterior basal body and a singlet root, both supporting a longitudinal channel or groove associated with the posterior flagellum. The anterior flagellar apparatus in each includes a root supporting structures to the left of the anterior flagellum. Given the probable deep divergences of Ancyromonas, apusomonads and excavates within eukaryotes, it is possible that the eukaryotic cenancestor also possessed these features.     

Reconstruction of the feeding apparatus in Postgaardi mariagerensis provides evidence for character evolution within the Symbiontida (Euglenozoa)

Microbial eukaryotes living in low oxygen environments often have novel physiological and morphological features that facilitate symbiotic relationships with bacteria and other means for acquiring nutrients. Comparative studies of these features provide evidence for phylogenetic relationships and evolutionary history. Postgaardi mariagerensis, for instance, is a euglenozoan that lives in low oxygen environments and is enveloped by episymbiotic bacteria. The general ultrastructure of P. mariagerensis was described more than a decade ago and no further studies have been carried out since, mainly because these cells are difficult to obtain. Postgaardi lacks the diagnostic features found in other major euglenozoan lineages (e.g., pellicle strips and kinetoplast-like mitochondrial inclusions) and no molecular data are available, so the phylogenetic position of this genus within the Euglenozoa remains unclear. We re-examined and reconstructed the ultrastructural organization of the feeding apparatus in Postgaardi by serial sectioning an existing block of resin-embedded cells. Postgaardi possesses distinctive finger-like projections within the feeding apparatus; this system has only been found in one other highly distinctive flagellate, namely the symbiontid Calkinsia. Detailed comparisons of the cytoskeleton in Postgaardi and in two symbiontids, Calkinsia and Bihospites, provided new evidence for phylogenetic relationships and character evolution in all three genera.     

The structure of the flagellar apparatus of the swarm cells ofPhysarum polycephalum

Summary Flagellation ofPhysarum polycephalum amoebae (Myxomycete) involves the formation around the two kinetosomes of a flagellar apparatus leading to a modification in the shape of the amoeba and its nucleus. A tridimensional ultrastructural model of the flagellar apparatus is proposed, based upon observation of the isolated nucleo-flagellar apparatus complex. The flagellar apparatus is composed of a non-microtubular structure (the posterior para-kinetosomal structure), five microtubular arrays and two flagella: a long anterior flagellum and a short flagellum directed backwards. The asymmetry of the flagellar apparatus is due mainly to the presence of the posterior para-kinetosomal structure on the right side of the posterior kinetosome and of the two asymmetrical microtubular arrays 3 and 4. Thus, the flagellar apparatus is right-handed. This asymmetry implies also some spatial constraints on two other microtubular arrays (2 and 5). Except in the case of the microtubular array 1 which links the proximal end of the anterior kinetosome to the nuclear membrane, the number of microtubules of each microtubular array seems to be well defined: 39, 5–6, 7–9, and 2+2 for the microtubular arrays 2, 3, 4, and 5 respectively. All the elements of the nucleo-flagellar apparatus complex are linked either directly or indirectly through bridges. Furthermore, the microtubules which composed the microtubular array 3 are linked through bridges while the microtubules of the microtubular arrays 2, 3, and 4 seem to be linked through a reticulate material. All these spatial relationships lead to a great cohesion of the nucleo-flagellar apparatus complex which appears to be a well defined structure. This suggests thatPhysarum amoebal flagellation can be a promising system to study the morphogenesis of an eucaryotic cell.Abbreviations PIPES Piperazine-N,N-bis [2-ethane-sulfonic acid] - EGTA [Ethylenebis(oxyethylenenitrile)]tetraacetic acid - DMSO Dimethyl sulfoxide     

Relationship between the flagellates and the ciliates.

The flagellates and the ciliates have long been considered to be closely related because of their unicellular nature and the similarity in the structures of the axoneme of the flagella and cilia in both groups. Most protozoologists believe that the ciliates arose from a flagellate. The flagellates that are most similar in structure to the ciliates are the dinoflagellates and two genera of uncertain taxonomic position, Colponema and Katablepharis. Structurally, dinoflagellates have a number of similarities with ciliates. These include the similarity of the cortical alveoli in the ciliates to the thecal vesicles in the dinoflagellates, the possession of tubular cristae, the similarity of the parasomal sac of the ciliates to the pusule of the dinoflagellates, the possession of similar trichocysts and mucocysts, and some similarity in the feeding apparatus. Colponema spp. are probably related to the dinoflagellates and have many of the same similarities with the ciliates. Katablepharis spp. are very similar in structure to the swarmer (embryo) of the suctorian ciliates. Indeed, reduction in the number of cilia to two in the suctorian swarmer and elimination of the macronucleus would result in a cell that is very similar to the Katablepharis cell. The feeding apparatus of Katablepharis spp. and the rest of the ciliates consists of two concentric microtubular arrays associated with vesicles. Information available from nucleotide sequencing of rRNA places the dinoflagellates in an ancestral position to the ciliates. The rRNA of Colponema and Katablepharis spp. has not yet been investigated. The use of stop codons in mRNA is discussed in relation to phylogeny.     

The flagellar apparatus of Breviata anathema,a eukaryote without a clear supergroup affinity

Breviata anathema is an anaerobic amoeboid flagellate that does not branch within any established ‘supergroup’. Molecular phylogenies suggest affinities to Amoebozoa, Opisthokonta, or apusomonads. Here we describe its flagellar apparatus ultrastructure. Breviata has two basal bodies. The flagellated anterior basal body (AB) is associated with a fan of ～18 microtubules and a short singlet microtubular root. Three microtubular roots associate with the posterior basal body. One, the right root (RR), is initially a triplet that splits into two parts. The other two are singlets: the left root (LR), and the middle root (MR), which arises on the posterior side of the basal body. The MR, LR and smaller part of RR support the left ventral side of the cell, while the larger part of RR runs down the right. Outer dynein arms were not observed on the flagellar axoneme. The mitochondrion-like organelle sometimes contains some tubular cristae. The posterior flagellar apparatus resembles that of several eukaryotic lineages, particularly apusomonads, ancyromonads, excavates, and myxogastrid amoebozoans. This comparison suggests that the complex flagellar apparatus of myxogastrids is actually plesiomorphic within Amoebozoa. The widely distributed splitting right root and posterior singlet (MR in Breviata) may be plesiomorphies in many eukaryotic lineages, and thus could be features of the last eukaryotic common ancestor.     

Hatena arenicola gen. et sp. nov., a katablepharid undergoing probable plastid acquisition

Hatena arenicola gen. et sp. nov., an enigmatic flagellate of the katablepharids, is described. It shows ultrastructural affinities to the katablepharids, including large and small ejectisomes, cell covering, and a feeding apparatus. Although molecular phylogenies of the 18S ribosomal DNA support its classification into the katablepharids, the cell is characterized by a dorsiventrally compressed cell shape and a crawling motion, both of which are unusual within this group. The most distinctive feature of Hatena arenicola is that it harbors a Nephroselmis symbiont. This symbiosis is distinct from previously reported cases of ongoing symbiosis in that the symbiont plastid is selectively enlarged, while other structures such as the mitochondria, Golgi body, cytoskeleton, and endomembrane system are degraded; the host and symbiont have developed a morphological association, i.e., the eyespot of the symbiont is always at the cell apex of Hatena arenicola; and only one daughter cell inherits the symbiont during cell division, resulting in a symbiont-bearing green cell and a symbiont-lacking colorless cell. Interestingly, the colorless cells have a feeding apparatus that corresponds to the location of the eyespot in symbiont-bearing cells, and they are able to feed on prey cells. This indicates that the morphology of the host depends on the presence or absence of the symbiont. These observations suggest that Hatena arenicola has a unique "half-plant, half-predator" life cycle; one cell divides into an autotrophic cell possessing a symbiotic Nephroselmis species, and a symbiont-lacking colorless cell, which later develops a feeding apparatus de novo. The evolutionary implications of Hatena arenicola as an intermediate step in plastid acquisition are discussed in the context of other examples of ongoing endosymbioses in dinoflagellates.     

Lotharella amoeboformis sp. nov.: A new species of chlorarachniophytes from Japan

The ultrastructure, morphology and life cycle of a new chlorarachniophyte alga collected from Okinawa in Japan have been studied. The life cycle of this alga consists of amoeboid, wall‐less round, coccoid and flagellated cells in culture condition; however, the coccoid and flagellate cells are very rare. The pyrenoid ultra‐structure of this alga is the same as that of a previously described species, Lotharella globosa. Since pyrenoid ultrastructure has been adopted as the main criterion for the generic classification of the chlorarachniophytes, the present alga is placed in Lotharella. However, the present alga has a dominant amoeboid cell stage and a reduced walled‐cell stage in the life cycle, while in L. globosa, the walled‐cell stage is dominant and there is no amoeboid cell stage. Therefore the present alga is described as a new species of Lotharella: Lotharella amoeboformis Ishida et Y. Hara sp. nov.     

The ultrastructure of the trophic cells of the protostelidPlanoprotθstelium aurantium

Summary The protostelidPlanoprotostelium aurantium Olive andStoianovitch has trophic cells which are either amoebae or flagellates. The general morphology and ultrastructure are consistent with what has been reported for otherEumycetozoa (protostelids, myxomycetes, and dictyostelids). The flagellar apparatus structure has the same basic pattern as that of other flagellate eumycetozoans. It shares with all these an anteriorly directed flagellum and centriole and microtubule arrays (MTA) 2–4. Unlike more primitive species which have two centrioles per flagellar apparatus,P. aurantium has only one. Also, the flagellar apparatus is independent of the nucleus inP. aurantium, not linked to it as in the primitive species. These features are useful in explaining the differences in swimming behavior betweenP. aurantium and biflagellate species. Evidence is presented to show thatP. aurantium is closely related to the non-flagellateProtostelium mycophaga Olive andStoianovitch.This research represents part of a Ph.D. dissertation presented to the University of North Carolina.     

The Morphology,Ultrastructure and SSU rRNA Gene Sequence of a New Freshwater Flagellate,Neobodo borokensis n. sp. (Kinetoplastea,Excavata)

A small free‐living freshwater bacteriotrophic flagellate Neobodo borokensis n. sp. was investigated by electron microscopy and analysis of its SSU ribosomal RNA gene. This protist has paraxonemal rods of typical bodonid structure in the flagella, mastigonemes on the proximal part of the posterior flagellum, two nearly parallel basal bodies, a compact kinetoplast, and discoid mitochondrial cristae. The flagellar pocket is supported by three microtubular roots (R1, R2 and R3) originating from the kinetosome. The cytopharynx is supported by the root R2, a microtubular prism, cytopharynx associated additional microtubules (CMT) and cytostome associated microtubules (FAS) bands. Symbiotic bacteria and small glycosomes were found in the cytoplasm. Cysts have not been found. The flagellate prefers freshwater habitats, but tolerates salinity up to 3–4‰. The overall morphological and ultrastructural features confirm that N. borokensis represents a new species of the genus Neobodo. Phylogenetic analysis of SSU rRNA genes is congruent with the ultrastructure and strongly supports the close relationship of N. borokensis to Neobodo saliens, N. designis, Actuariola, and a misidentified sequence of “Bodo curvifilus” within the class Kinetoplastea.     

Microtubules and the flagellar apparatus in zoospores and cysts of the fungusPhytophthora cinnamomi

Summary A correlated immunofluorescence and ultrastructural study of the microtubular cytoskeleton has been made in zoospores and young cysts ofPhytophthora cinnamomi. Labelling of microtubules using antibodies directed towards tubulin has revealed new details of the arrangement of the flagellar rootlets in these cells, and of the variability that occurs from cell to cell. Most of the variation exists at the distal ends of the rootlets, and may be correlated with differences in cell shape in these regions. The rootlets have the same right and left configuration in all zoospores. The arrangement of the rootlet microtubules at the anterior end of the zoospores raises the possibility that the microtubules on the left hand side of the groove may not comprise an independent rootlet which arises at the basal bodies.The absolute configuration of the flagellar apparatus has been determined from ultrastructural observations of serial sections. In the vicinity of the basal bodies, there is little, if any, variation between individuals, and the structure of the flagellar apparatus is similar to that described for related species of fungi. Two ribbon-like coils surround the central pair of microtubules at the distal tip of the whiplash flagellum, and clusters of intramembranous particles, similar to ciliary plaques, have been found at the bases of both flagella. There are two arrays of microtubules associated with the nucleus in the zoospores. One array lies next to the outer surface of the nuclear envelope, and probably functions in the shaping and positioning of the apex of the nucleus. The nuclear pores in this region are aligned in rows alongside these microtubules. The second array is formed by kinetochore microtubules which extend into a collar-like arrangement of chromatin material around the narrow end of the (interphase) nucleus. During encystment, all flagellar rootlets are internalized when the flagella are detached at the terminal plate. The rootlets arrays are no longer recognizable 5–10 minutes after the commencement of encystment.     

Ultrastructure of the amoeboid flagellate <Emphasis Type="Italic">Thaumatomonas zhukovi</Emphasis> Mylnikov et Mylnikov (Thaumatomonadida (Shirkina) Karpov, 1990)

The ultrastructure of the amoeboid flagellate Thaumatomonas zhukovi sp. is presented. The cell is covered by cell body scales that formed on the surface of mitochondria. Capturing bacteria, the pseudopodia emerge from the ventral groove, which is supported by two longitudinal microtubular bands. The heterodynamic flagella emerge from the small flagellar pocket. Both flagella are covered by cone-shaped scales and thin twisted mastigonemes. The transitional zone of the flagella contains a thin-walled cylinder. The transversal plate of the flagella rises above the cell surface. The kinetosomes lie parallel to each other. The flagellar root system consists of three microtubular bands and a fibrillar rhizoplast. The vesicular nucleus and the Golgi apparatus have typical structures. The cytoplasm contains microbodies and food vacuoles. Mitochondria contain tubular cristae. Extrusive organelles (kinetocysts), which contain amorphous material and a capsule, were found in the cytoplasm. The capsule consists of a theca and a cylinder. The resemblance of Thaumatomonas zhukovi to other thaumatomonads is discussed.     

Microtubular cytoskeletons of the trophic cells of five eumycetozoans

Summary The trophic cells of the protostelids,Ceratiomyxella tahitiensis, Cavostelium apophysatum, Planoprotostelium aurantium, andClastostelium recurvatum, and the reduced myxomycete,Echinostelium bisporum, were examined with indirect immunofluorescence to determine the overall structure of the microtubular cytoskeletons of each type of cell. All five species have a distinct flagellar apparatus in the amoeboflagellate state, but they vary with respect to the presence of body microtubules, those microtubules which do not focus on the flagellar apparatus. The obligate amoebae ofC. tahitiensis, C. apophysatum andC. recurvatum all have extensive microtubular cytoskeletons, but each is unique to its respective species. The obligate amoeba ofC. tahitiensis has scattered microtubules which often describe curved paths. The microtubules never appear to focus on MTOCs. The microtubular cytoskeleton ofC. apophysatum consists of relatively straight, rigid appearing microtubules. Small subpopulations of these microtubules radiate from MTOCs near the nucleus. The obligate amoeba ofC. recurvatum has a cytoskeleton consisting of numerous microtubules which radiate from a perinuclear MTOC and fill the body of the cell. These results correlate well with earlier ultrastructural observations which suggest that the amoeboflagellate state is homologous in these mycetozoans and that the obligate amoebae, when present, are unique to the various lineages in which they appear.     

ULTRASTRUCTURE OF THE FLAGELLA OF THE COLORLESS PHAGOTROPH PERANEMA TRICHOPHORUM (EUGLENOPHYCEAE).II. FLAGELLAR ROOTS1

Peranema trichophorum (Ehrenberg) Stein, a colorless phagotrophic euglenoid flagellate, has a typically euglenoid microtubular root complement. Striated root components, relatively uncommon in euglenoids, are connected to the basal bodies and to a microtubular root. The flagellar system of Peranema consists of three unequal microtubular roots which extend anteriorly beneath the reservoir membrane, and narrow-band striated roots (periodicity = 29–33 nm) which connect one of the four basal bodies to the movable rodorgan of the feeding apparatus. An inter basal body striated fiber forms a three-way connection between one particular microtubular root, a flagellar basal body, and the striated roots. A striated fibril (periodicity = 18–25 nm), which may be an extension of the striated root system, extends beneath the reservoir membrane. Associated with the striated fibril and the striated roots are cisternae of smooth endoplasmic reticulum.     

Spironucleus vortens (Diplomonadida) in the Ide,Leuciscus idus (L.) (Cyprinidae): a warm water hexamitid flagellate found in northern Europe

The hexamitid flagellate Spironucleus vortens, previously reported from Pterophyllum scalare from Florida, was found in the intestine of Leuciscus idus in Norway. The flagellate was cultivated and studied by scanning and transmission electron microscopy. Identification was based on a suite of ultrastructural features unique for S. vortens: compound lateral ridges, a swirled posterior end, and a distinctive microtubular cytoskeleton. Microfibrillar structures with a periodicity of 0.13 microm in the right peripheral part of the compound lateral ridges were shown to be responsible for the distinctive rope-like appearance of the peripheral ridge seen in scanning electron micrographs, and not previously reported for S. vortens. The present results show a wide geographic distribution and a wide temperature tolerance for S. vortens. The flagellate was successfully cultivated at 5 degrees C and 15 degrees C, having previously been cultivated between 2-34 degrees C. Spironucleus vortens is believed to be endemic in Norwegian waters, but an introduction hypothesis is also discussed. The similarity is striking between S. vortens and S. elegans, previously described from amphibians and fish in Europe, and the possibility of conspecificity is believed to be high.     

Flagellar and cytoskeletal systems in amitochondrial flagellates: Archamoeba,Metamonada and Parabasala

Summary The hypothesis that protists without mitochondria, the so-called Archezoa of Cavalier-Smith, are primitive has received some support from rRNA sequence studies on Microsporidia and Diplomonadida. In spite of the lack of mitochondria the archezoan groups of protists show considerable differences in their organization: mastigont and cytoskeletal system, mitosis, Golgi apparatus, hydrogenosomes. This paper examines the characters of the flagellar apparatus and its associated cytoskeleton to obtain clues used for phylogenetic consideration on the three cited groups of flagellates. Archamoebae of the Pelobiontida order comprising families such as Pelomyxidae and Mastigamoebidae share common features: a rudimentary mastigont system composed of only one basal body giving rise to a poorly motile flagellum and a basal body associated microtubular cone capping the nucleus. No Golgi apparatus has been detected.Metamonada, comprising three orders: Retortamonadida, Diplomonadida, and Oxymonadida, have been tentatively assembled on the basis of the absence of mitochondria, Golgi apparatus, and basal body arrangement. They all have four basal bodies arranged in two pairs with always one recurrent flagellum generally included in a cytostomal depression. The recurrent basal body/flagellum is in relation to recurrent microtubular fibers. However, they display marked differences in their cytoskeletal system and fiber ultrastructure indicating a distant evolutionary relationship. The presence of a corset of microtubules in retortamonads and three microtubular fibers are distinguished in diplomonads, as well as a paracrystalline preaxostyle and axostyle in oxymonads are features that lend support to these groups being highly divergent.Parabasala, comprising the orders Trichomonadida and Hypermastigida, is a monophyletic group with a set of homologous features such as the presence of the same arrangement of four basic basal bodies, the parabasal apparatus (striated fibre supporting Golgi), the microtubular pelta-axostyle complex, the external mitotic apparatus (crypto-pleuro-mitosis), the hydrogenosomes. These three phyla appear distantly related, the Parabasala being a homogeneous group, perhaps also the Pelobiontida, while the Metamonada is heterogeneous and composed of three evolutionary lineages. Additional information such as rRNA and protein sequence data could contribute to a better understanding of the phylogenetic relationships among these groups.Abbreviations EM electron microscopy - MTOC microtubule organizing centre - PF parabasal fibre