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11777 results in Plant sciences

Page 38 of 589

  • 9 - Cryptophyta

  • from Part V - Evolution of Two Membranes of Chloroplast Endoplasmic Reticulum and the Chlorarachniophyta
  • Robert Edward Lee, Colorado State University
  • Book:
    Phycology
    Published online:
    06 August 2018
    Print publication:
    01 March 2018, pp 309-317

  • Summary

    This group is composed primarily of flagellates that occur in both marine and freshwater environments. The cells contain chlorophylls a and c2 and phycobiliproteins that occur inside the thylakoids of the chloroplast. The cell body is asymmetric with clearly defined dorsi-ventral/right-left sides (Figs. 9.1, 9.6). The asymmetric cell shape results in a peculiar swaying motion during swimming. Most cryptophytes have a single lobed chloroplast with a central pyrenoid.

    Cell Structure

    There are two apically or laterally attached flagella at the base of a depression. Each flagellum is approximately the same length as the body of the cell (Figs. 9.1, 9.2, 9.6). The flagella are anchored in the cytoplasm by microtubular roots, striatedfiber roots, and a rhizostyle (Nam and Shin, 2016). Depending on the species, there are one or two rows of microtubular hairs attached to the flagellum. In Cryptomonas sp., the hairs on one flagellum are 2.5 μm long and in two rows whereas the hairs on the other flagellum are only 1μm long and arranged in a single row (Heath et al., 1970 ; Kugrens et al., 1987). Small organic scales 150 nm in diameter (Fig. 9.1) are common on the flagellar surface and sometimes on the cell body (Lee and Kugrens, 1986). The outer portion of the cell, or periplast (Gantt, 1971), is composed of the plasma membrane and a plate, or series of plates, directly under the plasma membrane, except under the furrow-gullet complex into which the contractile vacuoles empty (Figs. 9.1, 9.2) (Kugrens and Lee, 1987 ; Hoef- Emden, 2014). The number and shape of these plates are used to characterize genera taking into consideration that the haploid and diploid phases of a single genus can have different plates (Hoef- Emden and Melkonian, 2003). New periplast plates are added in an area adjacent to the vestibulum (Brett and Wetherbee, 1996). Sulfated fucose-rich polysaccharides can be excreted outside of the cell (Giroldo and Vieira, 2002).

    The chloroplast most likely evolved from a symbiosis between an organism similar to the phagocytic cryptomonad Goniomonas (Figs. 9.5, 9.6) and a red alga (Kugrens and Lee, 1991 ; Liaud et al., 1997 ; McFadden et al., 1994).

  • 5 - Chlorophyta

  • from Part III - Evolution of the Chloroplast
  • Robert Edward Lee, Colorado State University
  • Book:
    Phycology
    Published online:
    06 August 2018
    Print publication:
    01 March 2018, pp 133-230

  • Summary

    The Chlorophyta, or green algae, have chlorophylls a and b, and form starch within the chloroplast, usually in association with a pyrenoid. The Chlorophyta thus differ from the rest of the eukaryotic algae in forming the storage product in the chloroplast instead of in the cytoplasm. No chloroplast endoplasmic reticulum occurs around the chloroplasts. The green algae are classified with the embryophyte higher plants in the Viridiplantae.

    The Chlorophyta are primarily freshwater; only about 10% of the algae are marine, whereas 90% are freshwater (Smith, 1955). Some orders are predominantly marine (Caulerpales, Dasycladales, Siphonocladales), whereas others are predominantly freshwater (Ulotrichales, Coleochaetales) or exclusively freshwater (Oedogoniales, Zygnematales). The freshwater species have a cosmopolitan distribution, with few species endemic in a certain area. In the marine environment, the green algae in the warmer tropical and semitropical waters tend to be similar everywhere in the world. This is not true of the Chlorophyta in the colder marine waters; the waters of the Northern and Southern hemispheres have markedly different species. The warmer waters near the equator have acted as a geographical barrier for the evolution of new species and genera.

    Cell Structure

    In the Chlorophyta, no microtubular hairs occur on the flagella, although fibrillar hairs (Chlamydomonas) and Golgi-produced scales (Pyramimonas (Fig. 5.11), are present in some genera. Cell walls usually have cellulose as the main structural polysaccharide, although xylans or mannans often replace cellulose in the Caulerpales (Huizing et al., 1979). The primitive algae in the Prasinophyceae have extracellular scales, or a wall derived from interlacing scales, composed of acidic polysaccharides (Becker et al., 1996). Algae in the Volvocales have walls composed of glycoproteins (Goodenough and Heuser, 1985).

    Chloroplast pigments are similar to those of higher plants; chlorophyll a and b are present. The main carotenoid is lutein. The siphonaceous genera, as well as the unicells Tetraselmis and Mesostigma, are the only green algae to have siphonoxanthin (Fig. 5.1) and its ester siphonein (Yoshi et al., 2003). Accumulation of carotenoids occurs under conditions of nitrogen deficiency, high irradiance, or high salinity (Solovchenko et al., 2010).

  • 4 - Rhodophyta

  • from Part III - Evolution of the Chloroplast
  • Robert Edward Lee, Colorado State University
  • Book:
    Phycology
    Published online:
    06 August 2018
    Print publication:
    01 March 2018, pp 84-132

  • Summary

    The Rhodophyceae, or red algae, comprise the only class in the division Rhodophyta. The Rhodophyceae are probably one of the oldest groups of eukaryotic algae. The red algae are most likely directly descended from a cyanome in the Glaucophyta (see Chapter 3). It is likely that the first red alga evolved into an ecological niche that was unoccupied by cyanobacteria, the only extant photosynthetic alga that evolved oxygen. This ecological niche would have been in waters with a pH less than 5, which, for some unknown reason, cyanobacteria are not able to inhabit (Brock, 1973). Indeed, modern phylogenetic studies utilizing nucleic-acid sequencing have shown that Cyanidium, an alga that lives in acidic waters, is probably the oldest extant red alga (Oliveira and Bhattacharya, 2000).

    The Rhodophyceae lack flagellated cells, have chlorophyll a, phycobiliproteins, floridean starch as a storage product, and thylakoids occurring singly in the chloroplast.

    A majoity of seaweeds are red algae, and there are more Rhodophyceae (about 4000 species) than all of the other major seaweed groups combined. Although marine red algae occur at all latitudes, there is a marked shift in their abundance from the equator to colder seas. There are few species in polar and subpolar regions, where brown and green algae predominate, but in temperate and tropical regions they far outnumber these groups. The average size of the plants also differs according to geographical region. The larger species of fleshy red algae occur in cool–temperate areas, whereas in tropical seas the Rhodophyceae (except for massive calcareous forms) are mostly small, filamentous plants. The Rhodophyceae also have the ability to live at greater depths in the ocean than do members of the other algal classes. They live at depths as great as 200 m, an ability related to the function of their accessory pigments in photosynthesis. About 200 species of Rhodophyceae occur in freshwater, where they do not reach as great a size as the red seaweeds (Skuja, 1938). The majoity of freshwater red algae occur in running waters of small to midsized streams (Sheath and Hambrook, 1988). Few red algae occur at currents of less than 30 cm s −. This fast flow probably favors red algae because loosely attached competitors are washed out and because of a constant replenishment of nutrients and gases.

  • 19 - Heterokontophyta, Xanthophyceae

  • from Part V - Evolution of Two Membranes of Chloroplast Endoplasmic Reticulum and the Chlorarachniophyta
  • Robert Edward Lee, Colorado State University
  • Book:
    Phycology
    Published online:
    06 August 2018
    Print publication:
    01 March 2018, pp 401-411

  • Summary

    The Xanthophyceae contain primarily freshwater and terrestrial algae with a few marine representatives. The class has a poor fossil record. Studies based on molecular genetics indicate the Xanthophyceae probably originated in the Middle Triassic (223 Ma, million years ago)(Brown, 2010) and is most closely related to the Phaeophyceae (Ariztia et al., 1991 ; Potter et al., 1997). Although the class is commonly called the Xanthophyceae, the proper name is the Tribophyceae, since there is no genus in the class that can lend its name to Xanthophyceae (Hibberd, 1981).

    The class is characterized by motile cells with a forwardly directed tinsel flagellum and a posteriorly directed whiplash flagellum (Figs. 19.1, 19.4(c)). The chloroplasts contain chlorophylls a and c (Sullivan et al., 1990), lack fucoxanthin, and are colored yellowish-green. The eyespot in motile cells is always in the chloroplast (Figs. 19.1, 19.4(c)), and the chloroplasts are surrounded by two membranes of chloroplast endoplasmic reticulum. The outer membrane of the chloroplast E.R. is usually continuous with the outer membrane of the nucleus. In most non-motile cells the wall is composed of two overlapping halves (Figs. 19.2, 19.3).

    Cell Structure

    Cell Wall

    The cell walls of two Xanthophyceae, Tribonema (Fig. 19.2) (Cleare and Percival, 1973) and Vaucheria (Figs. 19.6, 19.7), are composed of cellulose (Parker et al., 1963). In Vaucheria cellulose comprises 90% of the wall, with the remaining portion being amorphous polysaccharides composed primarily of glucose and uronic acids. Many of the algae in the class have walls composed of two overlapping halves that fit together as do the two parts of the bacteriologist's Petri dish (Figs. 19.2, 19.3). The two-part nature of the wall cannot be delineated with the light microscope unless the cells have been treated with certain reagents such as concentrated potassium hydroxide. A typical example is the wall of Ophiocytium majus (one study places Ophiocytium in the closely related Eustigmatophyceae based on the sequence of mitochondrial cytochrome oxidase (Ehara et al., 1997)), which is tubular in shape (Fig. 19.3). The wall is composed of two parts, a cap of constant size fitted over a tubular basal portion.

  • 20 - Heterokontophyta, Phaeothamniophyceae

  • from Part V - Evolution of Two Membranes of Chloroplast Endoplasmic Reticulum and the Chlorarachniophyta
  • Robert Edward Lee, Colorado State University
  • Book:
    Phycology
    Published online:
    06 August 2018
    Print publication:
    01 March 2018, pp 412-414

  • Summary

    Recent nucleotide sequencing has uncovered an evolutionary line of golden-brown algae not related to other golden-brown algae (Bailey et al., 1998). These algae have been placed in the class Phaeothamniophyceae, a class that is most closely related to the Xanthophyceae and Phaeophyceae. The cytology of these three classes is similar (Fig. 20.1). The cells have two membranes of chloroplast endoplasmic reticulum with the outer membrane of chloroplast E.R. continuous with the outer membrane of the nuclear envelope. The chloroplasts have a ring-shaped genophore and girdle lamellae. The flagella are inserted laterally into the motile cells. The anterior tinsel flagellum has tripartite hairs that lack lateral filaments. The posterior flagellum lacks hairs. New daughter cells are formed by eleutheroschisis (parent cell wall is completely cast off and new daughter cell walls are formed). Vesicles under the plasma membrane appear similar to the physodes that occur in the Phaeophyceae. The Phaeothamniophyceae is the only class of algae where fucoxanthin and heteroxanthin occur together. Endogenous siliceous cysts (statospores) are not produced by these algae.

    Phaeothamnion is a filamentous brown alga that forms zoospores that settle to produce new filaments (Fig. 20.1) (Andersen et al., 1998). Tetrachrysis occurs in environments such as peat ponds and has cells embedded in a common mucilage (Dop et al., 1980) (Fig. 20.2). Tetrasporopsis is a colonial freshwater alga that consists of a brown, gelatinous, bladdery sac (Entwisle and Andersen, 1990) (Fig. 20.2). Phaeoschizochlamys occurs among detritus or suspended between other freshwater algae. The cells occur in mucilage of different shapes up to 0.5 mm in diameter (Fig. 20.2). The cells divide to form four autospores containing two chloroplasts.

  • Preface to the Fifth Edition

  • Robert Edward Lee, Colorado State University
  • Book:
    Phycology
    Published online:
    06 August 2018
    Print publication:
    01 March 2018, pp xi-xii

  • Summary

    It has been 45 years since I spent a considerable amount of time among the extensive collections in the old Cullen and the new Wartenweiler libraries at the University of the Witwatersrand in Johannesburg, writing and illustrating most of the first edition of Phycology. The illustrations were pen and ink, the photographs were done in the wet trays in the darkroom, and the text was written using a Smith Corona typewriter. The Smith Corona typewriter is presumably still in Iran as my family left with only three suitcases and could not carry the typewriter after sitting out the revolution in Shiraz and living under the clerical regime of Khomeini for a few months. We were probably one of the last American families to leave Shiraz. I had been a US Army platoon leader in Vietnam and the family had lived under UDI in Rhodesia, apartheid in South Africa, and had experienced the Portuguese African wars, so we weren't too rattled by the Iranian Revolution. However, after getting past the cordon of Soviet BTR-60 eight-wheeled armored cars and light Scorpion tanks surrounding the Shiraz airport, we were pleased to be getting on an airplane for Bahrain with the first edition of Phycology in hand.

    A lot has, of course, changed since then. No more typewriter, everything is done using Microsoft Word on the computer. No more pen and ink, drawings are now done with Adobe Illustrator. No more darkroom, photographs are digitally manipulated with Adobe Photoshop.

    The science of phycology has moved on also. In the first edition, the hot research papers were about life cycles and cytology using electron microscopes. These areas of research have now matured and do not generate anywhere near the levels of interest in the field. While the fifth edition of Phycology has generally updated the field, certain areas have received more attention. Specifically:

  • • The evolution of the chloroplast from cyanobacteria has rightly been extensively investigated since the process of photosynthesis is integral to the production of food stuffs for the world population. It has been known for some time that algal chloroplasts evolved from endosymbiotic cyanobacteria. However, it is only recently that many of the transport issues involving control of division and metabolism of chloroplasts has been elucidated, essential information in the understanding of photosynthesis.

  • 1 - Basic Characteristics of the Algae

  • from Part I - Introduction
  • Robert Edward Lee, Colorado State University
  • Book:
    Phycology
    Published online:
    06 August 2018
    Print publication:
    01 March 2018, pp 2-30

  • Summary

    Phycology or algology is the study of the algae. The word phycology is derived from the Greek word phykos, which means “seaweed.” The term algology, described in Webster's dictionary as the study of the algae, has fallen out of favor because it resembles the term algogenic, which means “producing pain.” The algae are thallophytes (plants lacking roots, stems, and leaves) that have chlorophyll a as their primary photosynthetic pigment and lack a sterile covering of cells around the reproductive cells. This definition encompasses a number of plant forms that are not necessarily closely related, for example, the cyanobacteria which are closer in evolution to the bacteria than to the rest of the algae.

    Algae most commonly occur in water, be it freshwater, marine, or brackish. However, they can also be found in almost every other environment on Earth, from the algae growing in the snow of some American mountains to algae living in lichen associations on bare rocks, to unicellular algae in desert soils, to algae living in hot springs. In most habitats they function as the primary producers in the food chain, producing organic material from sunlight, carbon dioxide, and water. Besides forming the basic food source for these food chains, they also form the oxygen necessary for the metabolism of the consumer organisms. In such cases, humans rarely directly consume the algae as such, but harvest organisms higher up in the food chain (i.e., fish, crustaceans, shellfish). Some algae, particularly the reds and browns, are harvested and eaten as a vegetable, or the mucilages are extracted from the thallus for use as gelling and thickening agents.

    Structure of the Algal Cell

    There are two basic types of cells in the algae, prokaryotic and eukaryotic. Prokaryotic cells lack membrane-bounded organelles (plastids, mitochondria, nuclei, Golgi bodies, and flagella) and occur in the cyanobacteria (Fig. 2.8). The remainder of the algae are eukaryotic and have organelles.

    A eukaryotic cell (Fig. 1.1) is often surrounded by a cell wall composed of polysaccharides that are partially produced and secreted by the Golgi body. The plasma membrane (plasmalemma) surrounds the remaining part of the cell; this membrane is a living structure responsible for controlling the influx and outflow of substances in the protoplasm. Locomotory organs, the flagella, propel the cell through the medium by their beating.

  • Part II - The Prokaryotic Algae

  • Robert Edward Lee, Colorado State University
  • Book:
    Phycology
    Published online:
    06 August 2018
    Print publication:
    01 March 2018, pp 31-31

  • Summary

    The cyanobacteria or blue-green algae form a natural group by virtue of being the only prokaryotic algae. Prokaryotic algae have an outer plasma membrane enclosing protoplasm containing photosynthetic thylakoids, 70S ribosomes, and DNA fibrils not enclosed within a separate membrane. Chlorophyll a is the main photosynthetic pigment, and oxygen is evolved during photosynthesis.

  • 3 - Glaucophyta

  • from Part III - Evolution of the Chloroplast
  • Robert Edward Lee, Colorado State University
  • Book:
    Phycology
    Published online:
    06 August 2018
    Print publication:
    01 March 2018, pp 80-83

  • Summary

    The Glaucophyta include those algae that have endosymbiotic cyanobacteria in the cytoplasm instead of chloroplasts. Because of the nature of their symbiotic association, they are thought to represent unsuccessful intermediates in the evolution of the chloroplast.

    The pigments of the Glaucophyta are similar to those of the Cyanophyceae: both chlorophyll a and the phycobiliproteins are present; however, two of the cyanobacterial carotenoids, myxoxanthophyll and echinenone, are absent (Chapman, 1966).

    Although similar to cyanobacteria, the cyanelles should be regarded as organelles rather than endosymbiotic cyanobacteria (Helmchen et al., 1995; McFadden, 2001). Cyanobacteria have over 3000 genes whereas cyanelles have about the same number of genes as plastids (about 200 genes). It is clear the cyanelle (and plastid) genomes have undergone substantial reduction during endosymbiosis. Many of the missing genes eventually relocated to the nucleus, while other genes were lost – made redundant in the cyanelles’ new role as an endosymbiont. For example, cyanobacteria have a respiratory electron-chain whereas plastids do not, the respiratory electronchain is coded by the nucleus in eukaryotic algae.

    The organisms in the Glaucophyta are very old; McFadden (2001) calls them the coelocanths of endosymbiosis. The Glaucophyta probably branched off the evolutionary tree before the divergence of red and green algae from one another (Keeling, 2004).

    The fact that in such syncyanoses one is dealing with composite organisms that exhibit features altogether new and no longer characteristic of either partner alone, led Skuja in 1954 to establish the phylum Glaucophyta. It must be appreciated that the organisms in the phylum represent a very old group, and that, when evolving, they were very plastic and undergoing a great deal of change in the attempt to reach the relatively stable level of a cell with a chloroplast. Such a dynamic group was formed consisting of a large number of organisms not well suited to compete with their more highly developed progeny. Such a situation led to the demise of many of the original members of the Glaucophyta, resulting in the existence today of few extant members of the group.

  • 17 - Heterokontophyta, Bacillariophyceae

  • from Part V - Evolution of Two Membranes of Chloroplast Endoplasmic Reticulum and the Chlorarachniophyta
  • Robert Edward Lee, Colorado State University
  • Book:
    Phycology
    Published online:
    06 August 2018
    Print publication:
    01 March 2018, pp 355-396

  • Summary

    The Bacillariophyceae or the diatoms probably evolved from a scaly member of the Chrysophyceae (similar to the organisms in the Parmales) or Bolidophyceae (Guillou et al., 1999 ; Medlin, 2016) around the Devonian–Carboniferous transition (360 Ma)(Brown, 2010). The diatoms are unicellular, sometimes colonial, algae found in almost every aquatic habitat as free-living photosynthetic autotrophs, colorless heterotrophs, or photosynthetic symbiotes (Schmaljohann and Rottger, 1978). They may occur as plankton or periphyton, with most brownish-green films on substrates such as rocks or aquatic plants being composed of attached diatoms. The cells are surrounded by a rigid two-part boxlike cell wall composed of silica, called the frustule. The chloroplasts contain chlorophylls a, c 1, and c 2 with the major carotenoid being the goldenbrown fucoxanthin, which gives the cells their characteristic color.

    In discussing diatoms and silica, there is often confusion over terminology in regard to silicon. Silicon is the element. Silica is a short convenient designation for silicon dioxide (SiO 2) in all of its crystalline, amorphous, and hydrated or hydroxylated forms. Silicate is any of the ionized forms of monosilicic acid [Si(OH) 4] (Iler, 1979).

    Cell Structure

    The two-part frustule surrounds protoplasm that has a more or less central nucleus suspended in a system of protoplasmic threads. The chloroplasts occupy most of the cell usually as two parietal plastids although sometimes as numerous discoid plastids. The storage product, chrysolaminarin, occurs in vesicles in the protoplasm.

    Cell Wall

    The characteristic feature of the Bacillariophyceae is their ability to secrete an external wall composed of silica, the frustule. It is constructed of two almost equal halves, the smaller fitting into the larger like a Petri dish (Figs. 17.1, 17.8, 17.9, 17.34). The outer of the two half-walls is the epitheca and the inner the hypotheca. Each theca is composed of two parts, the valve, a more or less flattened plate, and the connecting band, attached to the edge of the valve. The two connecting bands, one attached to each valve, are called the girdle (von Stosch, 1975). Sometimes the connecting bands themselves are called girdle bands (Fig. 17.34).

  • 6 - Euglenophyta

  • from Part IV - Evolution of One Membrane of Chloroplast Endoplasmic Reticulum
  • Robert Edward Lee, Colorado State University
  • Book:
    Phycology
    Published online:
    06 August 2018
    Print publication:
    01 March 2018, pp 235-249

  • Summary

    Euglenoid flagellates occur in most freshwater habitats: puddles, ditches, ponds, streams, lakes, and rivers, particularly waters contaminated by animal pollution or decaying organic matter (Buetow, 1968). Usually larger bodies of purer water, such as rivers, lakes, and reservoirs, have sparser populations of less common euglenoids as planktonic organisms. Marine euglenoids are more common than supposed, with Eutreptia, Eutreptiella (Figs. 6.8, 6.11(c)), and Klebsiella occurring exclusively in marine or brackish water, and many other genera having one or a few marine species. These occur in the open sea, in tidal zones among seaweeds, and as sand inhabitants on beaches. Brackish species of Euglena (Figs. 6.1, 6.2, 6.4, 6.11(a)) often color estuarine mud flats green when light intensity is low, the green color disappearing in full sunlight as the euglenoids creep away from the surface. There are also several parasitic euglenoid flagellates, mostly species of Khawkinea, Euglenamorpha, and Hegneria.

    Euglenoids are characterized by chlorophylls a and b, one membrane of chloroplast endoplasmic reticulum, a mesokaryotic nucleus, flagella with fibrillar hairs in one row, no sexual reproduction, and paramylon or chrysolaminarin as the storage product in the cytoplasm.

    Euglenoid cells have two basal bodies and one or two emergent flagella (Fig. 6.2). The flagella are similar to those of trypanosomes in having a paraxonemal rod (paraxial rod) that runs the length of the flagellum inside the flagellar membrane (Ngo and Bouck, 1998 ; Bastin and Gull, 1999 ; Talke and Preisfeld, 2002). The paraflagellar rod is composed of two major proteins forming an elongated alpha-helical stalk that parallels the axoneme. The one emergent flagellum in Euglena has helically arranged fibrillar hairs (no microtubules) attached along the length of the flagellar membrane. The fibrillar hairs are of two lengths: there is a single helical row of long (3 μm) hairs and two helical rows of short (1.5 μm) hairs in Euglena (Bouck et al., 1978). Other genera have flagella similar to Euglena (Hilenski and Walne, 1985). There are two basic types of flagellar movement in the class.

  • 14 - Heterokontophyta, Dictyochophyceae

  • from Part V - Evolution of Two Membranes of Chloroplast Endoplasmic Reticulum and the Chlorarachniophyta
  • Robert Edward Lee, Colorado State University
  • Book:
    Phycology
    Published online:
    06 August 2018
    Print publication:
    01 March 2018, pp 345-350

  • Summary

    These golden-brown algae are characterized by tentacles or rhizopodia on basically amoeboid vegetative cells (Moestrup, 1995 ; Preisig, 1995). Amoeboid cells are relatively rare among the algae, being mostly restricted to the Dictyochophyceae and the Xanthophyceae (Hibberd and Chretiennot-Dinet, 1979). The algae in the Dictyochophyceae have been previously classified in the Chrysophyceae, although molecular evidence shows them to be most closely related to the Pelagophyceae (Cavalier-Smith et al., 1995) or Eustigmatophyceae (Daugbjerg and Andersen, 1997).

    Classification

    The Dictyochophyceae can be divided into three orders (Preisig, 1995).

    Order 1 Rhizochromulinales : marine and freshwater unicells with tentacles.

    Order 2 Pedinellales : unicells with a long anterior flagellum and a second flagellum reduced to a basal body, usually three to six chloroplasts (if chloroplasts are present), marine and freshwater.

    Order 3 Dictyocales : marine unicells with an external silicified skeleton.

    Rhizochromulinales

    This order contains the more primitive organisms in the order (O'Kelly and Wujek, 1995). Rhizochromulina (Fig. 14.1(a), (b)) has amoeboid non-flagellated vegetative cells with many finebeaded filipodia and a single golden-brown chloroplast (Hibberd and Chretiennot-Dinet, 1979). The fusiform zoospore has a single tinsel flagellum with a second basal body in the protoplasm (Fig. 14.1(b)). Chrysoamoeba (Fig. 14.1(d)) lives as a solitary amoeba for the greater part of its life cycle, transforming into swimming cells with a single long flagellum only for short periods. In Phaeaster (Fig. 14.1(c)), the anterior portion of the cell is drawn out into rhizopodia.

    Pedinellales

    The pedinellids are unique in containing genera that are phototrophic (Apedinella (Fig. 14.2(c)), Pseudopedinella), mixotrophic (able to photosynthesize and take up organic compounds) (Pedinella) (Fig. 14.2(a), (b)), and phagotrophic (Pteridomonas, Ciliophrys). The phagotrophic genera have vestigial chloroplasts and evolved from genera with chloroplasts (Sekiguchi et al., 2002). The organisms in this order have three interconnected microtubules (triads) that course from the nuclear envelope through tentacles (if they are present) to the plasma membrane (Fig. 14.2(a)) (Daugbjerg, 1996).

Page 38 of 589