THE FLAGELLAR APPARATUS OF CHILOMONAS PARAMECIUM (CRYPTOPHYCEAE) AND ITS COMPARISON WITH CERTAIN ZOOFLAGELLATES1

The major components of the internal flagellar apparatus of Chilomonas paramecium Ehr. are two large microtubular roots and a striated root paralleled by three microtubules. The two microtubular roots overlap at the basal bodies. One microtubular root follows a curved path in the anterior of the cell, and the other extends straight to the posterior passing through a groove in the nucleus. The striated root extends laterally from the basal bodies. Except that it is smaller, the posteriorly directed root bears a strong resemblance to the axostyle of oxymonads. The overall arrangement and structure of the flagellar roots is similar to the pelta, axostyle and costa of trichomonads and the pelta and axostyle of oxymonads, groups of mitochondrion-less, largely parasitic or symbiotic protozoans. An affinity between cryptomonads and oxymonads or trichomonads would have many phylogenetic implications, some of which are discussed.     

Molecular phylogeny of three oxymonad genera: Pyrsonympha,Dinenympha and Oxymonas

Oxymonads are a morphologically well-characterized and highly diverse lineage of protists. They are, however, under sampled at a molecular level. It has recently been demonstrated that a genus of oxymonads, Pyrsonympha, is phylogenetically related to the excavate taxon Trimastix. Here, we addressed issues of internal oxymonad evolution. Pyrsonympha and Dinenympha are shown, by fluorescent in situ hybridization and phylogenetic evidence, to be separate genera and not morphotypes of the same organism. We demonstrated that three genera of oxymonads, Dinenympha, Pyrsonympha, and Oxymonas are each monophyletic and together form a clade which excludes other known eukaryotes. We have presented a taxonomic scheme of oxymonads taking into account their sisterhood with Trimastix and speculated on morphological evolution of oxymonads, particularly of their attachment apparatuses. Our biogeographical analysis with Japanese and Canadian Pyrsonympha and Dinenympha suggests that these genera diverged before the separation of termites that inhabit Eastern Asia and Western North America.     

The flagellates of the termite Hodotermopsis sjoestedti: Immunological and ultrastructural characterization of four new species in the genera Spirotrichonympha, Spironympha and Microjoenia

Four species of spirotrichonymphids representing three genera Spirotrichonympha, Spironympha and Microjoenia symbiotic in the termite Hodotermopsis sjoestedti, have been studied by light and immunofluorescence microscopy and transmission electron microscopy. The genus Spirotrichonympha represented by Spirotrichonympha cincta n. sp. is characterized by a compound axostyle composed of several fibers or subaxostyles, and this species has peculiar undescribed structures associated with the flagellar lines. The genus Spironympha is characterized by flagellar lines restricted to the anterior area and a simple tubular axostyle limited by 1–3 layers of microtubules. The two new Spironympha species Spironympha obtusa and Spironympha oblonga are distinguished by peculiarities in the flagellar lines and the axostyle, as revealed by immunofluorescence and electron microscopy. The genus Microjoenia represented by Microjoenia minuta n. sp. has radiating flagellar lines and an axostyle with two microtubular rows originating from the pelta-axostyle rows covering the anterior cap. Four new species were named and one was assigned to the SSU rRNA sequences provided by the molecular phylogenetic studies by Ohkuma et al. [2000. Phylogenetic identification of hypermastigotes, Pseudotrichonympha, Spirotrichonympha, Holomastigotes, and parabasalian symbionts in the hindgut of termites. J. Eukaryot. Microbiol. 47, 249–259; 2005. Molecular phylogeny of parabasalids inferred from small subunit rRNA sequences, with emphasis on the Hypermastigea. Mol. Phylogenet. Evol. 35, 646–655].     

Axostyle structure in the termite protozoon Pyrsonympha vertens

The axostyle of Pyrsonympha vertens is a cellular organelle composed of interconnected microtubules. In living organisms the axostyle has waves which originate at the anterior end of the protozoon and traverse the length to the posterior end of the protozoon so that an average of 3–4 waves are present in the organelle at any given point in time. The part of the axostyle between the waves is straight. In sections through the middle of the straight part, the microtubules are hexagonally packed, with predominant connections between tubules in rows across the width of the axostyle, but the microtubules are rectilinearly packed through the wave. The wave appears to involve changes in orientation and arrangement of the microtubules. The general structure of the microtubules, cross-bridges and axostyle in the straight and bent portions are described and related to the wave propagation by this organelle.     

Motility of the microtubular axostyle in Pyrsonympha

The rhythmic movement of the microtubular axostyle in the termite flagellate, Pyrsonympha vertens, was analyzed with polarization and electron microscopy. The protozoan axostyle is birefringent as a result of the semi-crystalline alignment of approximately 2,000 microtubules. The birefringence of the organelle permits analysis of the beat pattern in vivo. Modifications of the beat pattern were achieved with visible and UV microbeam irradiation. The beating axostyle is helically twisted and has two principal movements, one resembling ciliary and the other flagellar beating. The anterior portion of the beating axostyle has effective and recovery phases with each beat thereby simulating the flexural motion of a beating cilium. Undulations develop from the flexural flipping motion of the anterior segment and travel along the axostyle like flagellar waves. The shape of the waves differs from that of flagellar waves, however, and are described as sawtooth waves. The propagating sawtooth waves contain a sharp bend, approximately 3 micron in length, made up of two opposing flexures followed by a straight helical segment approximately 23 micron long. The average wavelength is approximately 25 micron, and three to four sawtooth waves travel along the axostyle at one time. The bends are nearly planar and can travel in either direction along the axostyle with equal velocity. At temperatures between 5 degrees and 30 degrees C, one sees a proportionate increase or decrease in wave propagation velocity as the temperature is raised or lowered. Beating stops below 5 degrees C but will resume if the preparation is warmed. A microbeam of visible light shone on a small segment of the axostyle causes the typical sawtooth waves to transform into short sine-like waves that accumulate in the area irradiated. Waves entering the affected region appear to stimulate waves already accumulated there to move, and waves that emerge take on the normal sawtooth wave pattern. The effective wavelengths of visible light capable of modifying the wave pattern is in the blue region of the spectrum. The axostyle is severed when irradiated with an intense microbeam of UV light. Short segments of axostyle produced by severing it at two places with a UV microbeam can curl upon themselves into shapes resembling lockwashers. We propose that the sawtooth waves in the axostyle of P. vertens are generated by interrow cross-bridges which are active in the straight regions.     

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     

Ultrastructure of the flagellar apparatus inPleurochrysis (classPrymnesiophyceae)

Summary The ultrastructure of the flagellar apparatus of aPleurochrysis, a coccolithophorid was studied in detail. Three major fibrous connecting bands and several accessory fibrous bands link the basal bodies, haptonema and microtubular flagellar roots. The asymmetrical flagellar root system is composed of three different microtubular roots (referred to here as roots 1,2, and 3) and a fibrous root. Root 1, associated with one of the basal bodies, is of the compound type, constructed of two sets of microtubules,viz. a broad sheet consisting of up to twenty closely aligned microtubules, and a secondary bundle made up of 100–200 microtubules which arises at right angles to the former. A thin electron-dense plate occurs on the surface of the microtubular sheet opposite the secondary bundle. The fibrous root arises from the same basal body and passes along the plasmalemma together with the microtubular sheet of root 1. Root 2 is also of the compound type and arises from one of the major connecting bands (called a distal band) as a four-stranded microtubular root and extends in the opposite direction to the haptonema. From this stranded root a secondary bundle of microtubules arises at approximately right angle. Root 3 is a more simple type, composed of at least six microtubules which are associated with the basal body. The flagellar transition region was found to be unusual for the classPrymnesiophyceae. The phylogenetic significance of the flagellar apparatus in thePrymnesiophyceae is discussed.     

The 3D Structure of the Apical Complex and Association with the Flagellar Apparatus Revealed by Serial TEM Tomography in Psammosa pacifica,a Distant Relative of the Apicomplexa

The apical complex is one of the defining features of apicomplexan parasites, including the malaria parasite Plasmodium, where it mediates host penetration and invasion. The apical complex is also known in a few related lineages, including several non-parasitic heterotrophs, where it mediates feeding behaviour. The origin of the apical complex is unclear, and one reason for this is that in apicomplexans it exists in only part of the life cycle, and never simultaneously with other major cytoskeletal structures like flagella and basal bodies. Here, we used conventional TEM and serial TEM tomography to reconstruct the three dimensional structure of the apical complex in Psammosa pacifica, a predatory relative of apicomplexans and dinoflagellates that retains the archetype apical complex and the flagellar apparatus simultaneously. The P. pacifica apical complex is associated with the gullet and consists of the pseudoconoid, micronemes, and electron dense vesicles. The pseudoconoid is a convex sheet consisting of eight short microtubules, plus a band made up of microtubules that originate from the flagellar apparatus. The flagellar apparatus consists of three microtubular roots. One of the microtubular roots attached to the posterior basal body is connected to bypassing microtubular strands, which are themselves connected to the extension of the pseudoconoid. These complex connections where the apical complex is an extension of the flagellar apparatus, reflect the ancestral state of both, dating back to the common ancestor of apicaomplexans and dinoflagellates.     

THE MICROTUBULAR CYTOSKELETON OF AMPHIDINIUM RHYNCHOCEPHALUM (DINOPHYCEAE)1

The sub-thecal microtubular cytoskeleton of Amphidinium rhynchocephalum Anissimowa was investigated using indirect immunofluorescence microscopy and transmission electron microscopy. The majority of sub-thecal microtubules are longitudinally oriented and radiate from one of two sub-thecal transverse microtubular bands that lie adjacent to the anterior and posterior edge of the cingulum.Both transverse bands consist of 3–5 microtubules and are loop shaped with one end adjacent to the cell's right edge of the sulcus and the other end adjacent to the fibrous ventral ridge. The posterior transverse microtubular band (PTB) defines the posterior edge of the cingulum and gives rise to numerous posteriorly directed longitudinal microtubular bundles that consist of 1–3 microtubules per bundle. These bundles end at the posterior end of the cell. The PTB also gives rise to the cingular longitudinal microtubules that underlie the cingular groove and terminate at the anterior transverse microtubular band (ATB). The ATB defines the anterior edge of the cingulum and loops around the base of the epicone. This band gives rise to anteriorly directed longitudinal microtubular bundles that terminate in the small epicone of the cell. The longitudinal microtubular root of the flagellar apparatus is directed posteriorly and lies immediately beneath the theca but is distinct from the subthecal microtubule system. A narrow fibrous ridge is ventrally located to the cell's left between the exit apertures of the transverse and longitudinal flagella. In this position, the ventral ridge lies between and also connects with the anterior and posterior transverse microtubular bands. The ventral ridge is also associated with three microtubules that are distinct from other cytoskeletal microtubules. Our results demonstrate that the majority of sub-thecal microtubules originate from one of two microtubular bands associated with the cingulum. The possible role of the fibrous ventral ridge and its associated microtubules is also discussed.     

Fine Structure of Bodo curvifilus Griessmann (Kinetoplastida: Bodonidae)*

SYNOPSIS. Bodo curvifilus Griessmann conforms in its fine structure to the criteria proposed for the genus Bodo, including the presence of subpellicular microtubules, a single large kinetoplast-mitochondrion, emergence of the 2 heterodynamic flagella from a subapical flagellar pocket, and the presence of a paraxial rod associated with the axoneme of each flagellum. B. curvifilus possesses cytoplasmic bodies which resemble endosymbiotic bacteria. These are similar to those found in Bodo saltans. Bodo curvifilus can be distinguished ultrastructurally from Bodo caudatus and B. saltans by the presence in B. curvifilus of a hitherto unreported structure, “the microtubular prism,”consisting of a bundle of 19 microtubules. In cross section, 15 of these microtubules form a cross-linked prismatic array. This microtubular bundle originates near the flagellar pocket and extends for several micrometers into the body of the organism where it follows the periphery of the cell and the long finger-like projections of the kinetoplast-mitochondrion.     

ISOLATION AND REACTIVATION OF THE AXOSTYLE : Evidence for a Dynein-like ATPase in the Axostyle

The contractile axostyle is a ribbon-shaped organelle present in certain species of flagellates found in the hindgut of wood eating insects. This organelle propagates an undulatory wave whose motion, like flagella and cilia, is related to microtubules. Unlike the axoneme of cilia and flagella, however, the axostyle is composed of singlet microtubules linked together in parallel rows. Axostyles were isolated from Cryptocercus gut protozoa with Triton X-100. Normal motility of the isolated axostyle could be restored with adenosine triphosphate (ATP); the specific conditions necessary for this reactivation were essentially identical with those reported for the reactivation of isolated flagella or whole sperm. ATPase activity of the isolated axostyle was comparable to the values reported for ciliary or flagellar axonemes. The axostyle was reasonably specific for ATP. Most of the proteins of the isolated axostyle comigrated with proteins of the ciliary axoneme on sodium dodecyl sulfate (SDS) polyacrylamide gels (i e. equivalent molecular weights). These included the following: the higher molecular weight component of dynein, tubulin, linkage protein (nexin), and various secondary proteins. Evidence for dynein in the axostyle is presented and a model proposed to explain how repeated propagated waves can be generated.     

THE AXOSTYLE OF SACCINOBACULUS : I. Structure of the Organism and Its Microtubule Bundle

The axostyle of the flagellate Saccinobaculus is a motile ribbon composed of microtubules, cross-bridged to form interconnected rows. We find a centriole-related row of dark-staining tubules near the nucleus at the anterior end of the axostyle. Other tubule rows bind parallel to this primary row, acquire ordered relationships, and become the tubules of the axostyle proper. The number of tubule rows is constant in Saccinobaculus lata from the region near the nucleus to within a few micrometers of the posterior tip of the cell. In Saccinobaculus ambloaxostylus a few tubule rows are added to the axostyle posterior to the nucleus, giving this axostyle a leaf spring construction. The tubules of S. lata are held in rows by links with a 140 Å periodicity along the tubule axis; bridges between rows of tubules are also seen but are not apparently periodic. Each tubule in S. ambloaxostylus shows an axial periodicity of 150 Å due to pairs of arms, one of which is always part of the intrarow link. Interrow bridges in this species run either from tubule to tubule or from tubule to the free arm, but as in S. lata they do not display an obvious axial periodicity. An average unit cell is presented for the axostyle of each species, and the relation of the intertubule links to the microtubule substructure is discussed.     

Colonization of termite hindgut walls by oxymonad flagellates and prokaryotes in Incisitermes tabogae,I. marginipennis and Reticulitermes flavipes

We studied the colonization of the paunch wall of three lower termites, Reticulitermes flavipes, Incisitermes tabogae, and Incisitermes marginipennis, by light and electron microscopy. In addition to various prokaryotes, oxymonad flagellates were attached to the wall of the paunch in all three species. The prokaryotic layer found in R. flavipes is relatively thin, since most organisms are attached laterally. Large members of the flagellate genus Pyrsonympha protrude into the gut lumen. The prokaryotes are very abundant on the gut wall in I. tabogae and I. marginipennis, forming a thick carpet of mostly vertically attached rods and wavy spirochetes. The adhering oxymonads are relatively small and almost hidden in the thick bacterial biofilm. Three small morphotypes were seen in I. tabogae; two possessing a short rostellum and one amoeboid. The only oxymonad found in I. tabogae so far, Oxymonas clevelandi, is not identical to any of the present oxymonads. I. marginipennis contains a mid-sized oxymonad with ectobiotic spirochetes, probably identical to Oxymonas hubbardi, and a tiny unknown morphotype. The spatial organization of the pro- and eukaryotic microorganisms on the gut wall of the three termites is described and discussed concerning oxygen stress.     

ULTRASTRUCTURE OF THE BASAL APPARATUS AND PUTATIVE VESTIGIAL FEEDING APPARATUSES IN A QUADRIFLAGELLATE EUGLENOID (EUGLENOPHYTA)1

The flagellar apparatus and presumptive vestigial feeding apparatuses of a cold-water, photosynthetic, quadriflagellate euglenoid is described. The organism possesses two similar sets of flagella each consisting of one short and one long flagellum. Each pair of flagella is associated with three microtubular roots for a total of six roots in the basal apparatus. At the level of the ventral basal bodies, each intermediate root is nine-membered, while the ventral roots are composed of eight to nine microtubules. Only one of the ventral roots lines the single microtubule reinforced pocket. A four-membered dorsal root attaches to each dorsal basal body, and at the level of the reservoir each gives rise to a dorsal band. An additional bundle of microtubules, not arising from the microtubular roots of the basal apparatus, begins posterior to the basal apparatus as a small group of a few microtubules and extends anteriorly on the right ventral side of the reservoir ending at the canal. At the level of the stigma, the microtubules are organized into a multi-layered bundle that continues to increase in size and eventually splits to form two bundles at the level of the canal. We postulate that these bundles may represent the remnants of a rod-and-vane-type feeding apparatus like that found in many phagotrophic euglenoids.     

THE FLAGELLAR APPARATUS OF OXYRRHIS MARINA (PYRROPHYTA)1

The three-dimensional structure of the flagellar apparatus in the dinoflagellate Oxyrrhis marina has been reinvestigated and found to consist of several previously unknown components and component combinations that appear strikingly similar to those of some gymnodinoid taxa. The flagellar apparatus of this dinoflagellate is asymmetric and extremely complex consisting of a longitudinal and a transverse basal body that gives rise to eight structurally different components. The only posteriorly directed component is the large microtubular root that consists of 45–50 microtubules at its origin and is attached proximally to a perpendicularly oriented striated fibrous component. Arising from each basal body, two striated fibrous roots with different periodicities extend to the cell's left. A single stranded microtubular root with associated electron dense material emanates from the transverse basal body and also extends to the cell's left. A striated fibrous connective arises from the longitudinal basal body and extends toward the cell's right ventral surface and terminates near the sub-thecal microtubular system. A compound root consisting of microtubules and electron dense material also originates from the longitudinal basal body and extends ventrally into the anterior region of the tentacle. Structural similarities between the parallel striated fibrous roots of Oxyrrhis and Polykrikos are discussed as are flagellar apparatus similarities among other gymnodinoid dinoflagellates. A diagrammatic reconstruction of the Oxyrrhis flagellar apparatus is also presented.     

An immunofluorescent study of the microtubule organization in Trichomonas vaginalis using antitubulin antibodies

The flagellated protozoon Trichomonas vaginalis, parasite of the human urogenital tract, possesses a well developed microtubule system organized in highly differentiated structures. We have shown by immunoblotting that monospecific anti-sheep brain tubulin antibodies are able to react with the microtubular tubulin of T. vaginalis. These antibodies were used to study the microtubular system of T. vaginalis both in interphase and mitosis by indirect immunofluorescence. The interphase microtubular pattern, characterized by an axostyle, a pelta, four anterior flagella, and a recurrent flagellum, displayed remarkable changes at the onset of mitosis: the axostyle disappeared, and two pole bodies connected by a short spindle became evident; chromosomal fibers arose while pole-to-pole fibers elongated. The last phases of mitosis were marked by the disappearance of chromosomal fibers, the appearance of two small axostyles, and the depolymerization of the pole-to-pole bundle. At the end of mitosis, the normal interphase microtubule pattern was observed.     

Pachyjoenia howa,a new symbiotic parabasalid joeniid flagellate of the termite Postelectrotermes howa

The Joenia-like lophomonad of Postelectrotermes howa is identified by light and electron microscopy as a new genus and species Pachyjoenia howa. Its flagellar area of about 1800 flagella is dome shaped. Basal bodies bear a composite root oriented counterclockwise in addition to the clockwise hook-shaped lamina present in other joeniids. There are four parallel privileged basal bodies. The main parabasal fibre is twisted around the axostyle and splits into several branches bearing Golgi bodies. The axostyle trunk is conspicuous and composed of a bundle of ∼90 small axostyles. There are sausage-shaped bacterial endosymbionts mixed with hydrogenosomes in the cytoplasm and coccoid bacterial endobionts in the nucleus. The characters of this new joeniid genus are compared with those of other joeniid genera.     

An Immunofluorescent Study of the Microtubule Organization in Trichomonas vaginalis Using Antitubulin Antibodies1

ABSTRACT. The flagellated protozoon Trichomonas vaginalis, parasite of the human urogenital tract, possesses a well developed microtubule system organized in highly differentiated structures. We have shown by immunoblotting that monospecific anti-sheep brain tubulin antibodies are able to react with the microtubular tubulin of T. vaginalis. These antibodies were used to study the microtubular system of T. vaginalis both in interphase and mitosis by indirect immunofluorescence. The interphase microtubular pattern, characterized by an axostyle, a pelta, four anterior flagella, and a recurrent flagellum, displayed remarkable changes at the onset of mitosis: the axostyle disappeared, and two pole bodies connected by a short spindle became evident; chromosomal fibers arose while pole-to-pole fibers elongated. The last phases of mitosis were marked by the disappearance of chromosomal fibers, the appearance of two small axostyles, and the depolymerization of the pole-to-pole bundle. At the end of mitosis, the normal interphase microtubule pattern was observed.     

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.     

THE FLAGELLAR APPARATUS OF GYMNODINIUM SP. (DINOPHYCEAE)1

The detailed structure of the flagellar apparatus has been determined in a small dinoflagellate of the genus Gymnodinium. Although diminutive, this dinoflagellate possesses a complex flagellar apparatus consisting of a posteriorly directed microtubular root, a transverse striated fibrous root, several striated fibrous connectives that attach the basal bodies to one another as well as to the different roots, and a conspicuous non-striated fibrous connective that directly links the posteriorly directded microtubular root with the extended lobe of the nucleus. This represents the second discovery of a nuclear connective linked to the flagellar apparatus in the Dinophyceae but is the first report to elucidate the spatial relationships of the connective with the flagellar apparatus and the cell. A detailed diagrammatic reconstruction is provided and the similarities between these flagellar apparatus features are compared with those known for other dinoflagellates. Additionally, the structure and displacement of the nuclear connective are compared with nuclear connectives described in other protists.