Helge Abildhauge Thomsen

An ultrastructural study of the flagellatePyramimonas orientalis with particular emphasis on Golgi apparatus activity and the flagellar apparatus

SummaryThe prasinophycean flagellatePyramimonas orientalis has been examined by light and electron microscopy of wild and cultured material. The many different scales which cover all cell surfaces, including the flagella, are described; their synthesis and assembly in the two Golgi bodies have been examined. The Golgi bodies work simultaneously to produce all-at least five—scale categories, including hollow hair shaped scales. From the Golgi system the scales become transported to a special container—a reservoir—in which they, in an unknown way, separate and become arranged in the same pattern as on the body surface. From the reservoir, the scales move through a duct to the cell surface, apparently together with the subtending membrane, which thus becomes incorporated in the plasmalemma or the flagellar membrane. The liberation process, which differs from that of other species ofPyramimonas examined, is illustrated diagrammatically, starting at two extensions of ER from the nuclear envelope.The flagellar apparatus possesses a flagellar root system of the green algal type, a finding of phylogenetic significance. Furthermore, near the flagellar transition region a structure was observed, which at present is known from certain “brown” groups of algae, but never from any green flagellate. The taxonomic implications are discussed briefly, and a virus attacking the nuclear area of the cell is reported. Very surprisingly two different sizes of the virus were found, which may be different stages of the same “organism”.

Telonemia, a new protist phylum with affinity to chromist lineages.

Recent molecular investigations of marine samples taken from different environments, including tropical, temperate and polar areas, as well as deep thermal vents, have revealed an unexpectedly high diversity of protists, some of them forming deep-branching clades within important lineages, such as the alveolates and heterokonts. Using the same approach on coastal samples, we have identified a novel group of protist small subunit (SSU) rDNA sequences that do not correspond to any phylogenetic group previously identified. Comparison with other sequences obtained from cultures of heterotrophic protists showed that the environmental sequences grouped together with Telonema, a genus known since 1913 but of uncertain taxonomic affinity. Phylogenetic analyses using four genes (SSU, Hsp90, alpha-tubulin and beta-tubulin), and accounting for gamma- and covarion-distributed substitution rates, revealed Telonema as a distinct group of species branching off close to chromist lineages. Consistent with these gene trees, Telonema possesses ultrastructures revealing both the distinctness of the group and the evolutionary affinity to chromist groups. Altogether, the data suggest that Telonema constitutes a new eukaryotic phylum, here defined as Telonemia, possibly representing a key clade for the understanding of the early evolution of bikont protist groups, such as the proposed chromalveolate supergroup.

The Baltic Sea ice Biota (March 1994): A study of the Protistan community

Summary The diversity of the protist communities of the water column and ice along the Finnish coast of the Baltic Sea was studied during March 1994. The preliminary identification of the organisms was made light microscopically on live material, while further identification of e.g. scale-bearing flagellates was based on whole mounts using light and electron microscopy. The ice biota and the winter plankton was dominated by diatoms. Other abundant groups were choanoflagellates, chrysophytes, chlorophytes, dinoflagellates and protists of uncertain affinity. The highest brine salinities (up to 30%o) and the most diverse ice biota were found at two stations in the Bothnian Bay, where the number of recorded taxa was 71 and 74. In the water column the numbers were much lower (34 and 42). In the Bothnian Sea and along the southern coast of Finland the ice biota was less diverse, and the number of protist taxa ranged from 21 to 47. A few taxa showed a special preference for the ice habitat. New distribution records to the Baltic Sea are Navicula pelagica (Bacillariophyceae), Cryothecomonas armigera (Protista incertae sedis), and the genus Polytomella (Chlorophyceae). The abundance and vertical distribution of C. armigera , other flagellates, Monoraphidium contortion (Chlorophyceae), and diatoms in the ice at station I was studied using inverted light microscopy and sedimentation chambers. M. contortum was found to be the cause of a distinct green colouration of the ice. With the exception of C. armigera , all other protist taxa formed well-defined maxima within the ice interior. The number of cells in such abundance peaks varied from approximately 2.5×10 5 M. contortum cells 1 −1 to 2×10 6 diatoms 1 −1 of melted sea ice.

Nanoplankton of the equatorial Pacific with emphasis on the heterotrophic protists

Abstract In the equatorial Pacific during the boreal spring of 1992, nanoplankton, represented by chrysophytes, dinoflagellates, amoebae, choanoflagellates, naked flagellates and ciliates, dominated the heterotrophic protistan biomass. This component contributed 11–60% of the combined phytoplankton and heterotrophic protistan biomass. The heterotrophs, other than the dinoflagellates and ciliates, were represented by amoebae and flagellates at a mean (±SD) density and biomass of 5.85 ± 2.53 x 105 cells I −1 and 1.76 ± 1.37 μgC l −1 . Fifty-two species of lobose amoebae, apusomonads, bicosoecids, cercomonads, choanoflagellates, chrysomonads, euglenids, jakobids, kathablepharids, kinetoplastids, pedinellids and a number of taxa of uncertain position (incertaesedis taxa) were identified. The heterotrophs represent five different trophic types of organisms, defined by habitat and prey. Fifty per cent of the species identified in this study are principally associated with detritus (marine snow). The majority of free-living suspension feeders we identify in this study are choanoflagellates. Other suspension feeding planktonic taxa may not be detected using the protocols we employ. Only 42% of the species identified are obligately bacterivorous and 12% are not bacterivores at all but graze principally on algae. The remainder of heterotrophic species prey on an array of DOM, bacteria, other protists and detritus.

HETEROMORPHIC LIFE HISTORIES IN ARCTIC COCCOLITHOPHORIDS (PRYMNESIOPHYCEAE)1

During three visits to Disko Bay, West Greenland, we found four different types of prymnesiophyte flagellates with heterococcoliths from species of the genera Papposphaera Tangen and Pappomonas Manton and Oates in characteristic and consistent combinations with holococcoliths from species of the genera Turrisphaera Manton, Sutherland, and Oates and Trigonaspis Thomsen. We conclude that several taxa previously considered to be autonomous species are, in fact, part of life histories combining hetero‐ and holococcolithophorid forms in a manner somewhat similar to that known from studies of cultured strains of Coccolithus pelagicus (Wallich) Schiller and Crystallolithus hyalinus (Gaarder) Markali. Similarly, Calciarcus Manton, Sutherland and Oates and Wigwamma Manton, Sutherland and Oates also may be alternate phases of a coccolithophorid life history.

An ultrastructural survey of the chrysophycean genus Paraphysomonas under natural conditions

Electron microscopical examination of whole mounts, prepared from freshly collected seawater samples from the Isefjord area (Denmark), has led to the enumeration of seven species belonging to the chrysophycean genus Paraphysomonas. One of these is P. sideriophora sp. nov., characterised by its single type of scale, each resembling a flat-iron. Three of the species have previously been recorded from Denmark. Most of the type descriptions of Paraphysomonas species refer to accidentally cultured material. When the same species are observed under natural conditions, as in the present investigation, the variation in scale size and morphology is seen to be considerably wider than reported in the type descriptions. This applies in particular to P. foraminifera Lucas and P. imperforata Lucas. The discrepancies between the type descriptions and the present material is probably a reflection of the fact that cultured material consists of one or a few clones only (sexual reproduction is unknown), whereas the immediat...

Nanoflagellates of the central California waters: taxonomy, biogeography and abundance of primitive, green flagellates (Pedinophyceae, Prasinophyceae)

Abstract Examination of whole mounts of cells prepared from samples collected off central California, September 1989, has led to the identification of 14 taxa of primitive green nanoflagellates from the Pedinophyceae (1 species) and the Prasinophyceae (13 species). Three of the prasinophyte taxa are new to science. The finding of these new taxa, provisionally identified as Prasinophyte “Point Sur” sp. 1, 2, 3, is important because it emphasizes the persistent, overall lack of knowledge of prasinophyte biodiversity, and also because these forms combine prasinophycean features in a unique way that ultimately may question the currently accepted taxonomic system. The abundance estimates suggest that prasinophytes are most numerous in coastal waters and are relatively absent from oceanic regimes.

Loricate choanoflagellates (Acanthoecidae, Choanoflagellida) from the Weddell Sea, Antarctica

A study of the choanoflagellate species composition of an Antarctic ice edge zone (northern Weddeil Sea, March 1986) has resulted in the finding of 16 taxa of which one, Cosmoeca takahashii Thomsen sp.n., is described here. An emended description is given of Parvicorbicula circularis. Morphological, numerical and dimensional aspects of other species have been analysed in an attempt to improve the circumscription of certain taxa, and to increase our understanding of the nature of intraspecific variability. Data on the relative abundance of choanoflagellate species along seaward transects perpendicular to the ice edge showed that seven species account for more than 95% of all choanoflagellates identified. The two most abundant species were Parvicorbicula socialis and Diaphanoeca pedicellata.

Choanoflagellates (acanthoecidae, choanoflagellida) from the Weddell Sea, Antarctica, Taxonomy and community structure with particular emphasis on the ice biota; with preliminary remarks on choanoflagellates from Arctic sea ice (Northeast Water Polynya, Greenland)

Summary Ice biota studies in the Antarctic region, Weddell Sea, have focused on an examination of single cells and an analysis of community structure of the flagellate assemblage from sea ice and comparisons with planktonic assemblages. Based on extensive light microscopical analysis of 40 samples ranging from open water to “brown-ice” habitats, it became evident through clustering of the data, that the mature choanoflagellate community from ice is significantly different from both the water column community and those encountered in samples derived from newly formed ice (i.e. grease ice, platelet ice, nilas and thin pancakes). The choanoflagellates from sea ice encompasses a range of previously undescribed loricate taxa ( Acanthocorbis nana sp. nov., A. weddellensis sp. nov., A. prolongata sp. nov., Apheloecion antarctica sp. nov., A. glacialis sp. nov., A. conicoides sp. nov., Calliacantha frigida sp. nov., C. ankyra sp. nov., Diaphanoeca multiannulata subsp. nov. glacialis, Parvicorbicula corynocostata sp. nov., P. pachycostata sp. nov.). These taxa have been investigated using a combination of light, and electron microscopy. A preliminary investigation of samples from the Arctic (NE Greenland) indicates that the loricate choanoflagellate diversity is significantly lower in Arctic sea ice.

Ultrastructural studies of the flagellate and cyst stages of Pseudopedinella tricostata (Pedinellales, Chrysophyceae)

During the winter of 1985 the uppermost part of the water column of the ice-covered Danish fjord, Isefjorden, was coloured yellowish brown by a growth of the small flagellate Pseudopedinella tricostata (ca. 75 × 106 cells 1-1). The species differs from others of the genus by having three chloroplasts only, each with an embedded pyrenoid. In March a distinct yellowish band was found in the lower part of the ice which electron microscopical examination showed to be due to the presence of millions of cysts of P. tricostata. The P. tricostata cyst has a continuous three-layered wall, thus differing markedly from the typical bipartite chrysophycean cyst. The outermost wall-layer contains a significant amount of iron.