The Phytoplankton: Euglenophyta, Pyrrhophyta and Stramenopiles

The Phytoplankton: Euglenophyta, Pyrrhophyta and Stramenopiles
Organisms termed planktonic include both “plant” and “animal”-like organisms and span from
the Eubacteriae (cyanobacteria) and Protista (euglenophyta, pyrrhophytae, stramenopiles and
(chlorophyta). Since the surface of the earth in its majority is covered in marine/brackish waters
(more than 70%) these types of life forms are innumerable.
In this course we will, of course, cover the autotrophs or phytoplankton, which is responsible for
the genesis of approximately 70% of the world’s atmospheric oxygen. For these organisms to
inhabit the open water, it is pertinent that they remain in the upper waters that have the highest
light intensity (euphotic zone). However, since the euphotic zone is prone to turbulence (induced
by wind, tide, etc.) remaining in the euphotic zone is an active process. It may be accomplished
by many adaptive mechanisms alone or in combination, including flagellation, microscopic size
(high surface area/volume, sinking increases with increased diameter), adaptive cell shape and
reduced cell densities (lighter). Therefore the majority of organisms in the plankton are
unicellular. The most prevalent in the marine phytoplankton are the dinoflagellates (10-80 µm)
and the diatoms (20-100 µm). Morphological designs that deviate from the regular centric or
spherical shape reduce sinking rates, which is especially obvious in the diatoms. Other unrelated
algal groups such as the dinoflagellates and euglenoids have evolved lighter, “naked” or
unarmored unicellular organisms, some of which are capable of shape changes.
Additionally, large nutrient quantities and other optimal conditions will lead to generation times
between 4-24 hrs which may be translated into changes in cell shape, size or densities. Many
species also include lifecycle stages that are induced during less than optimal environmental
conditions. These stages, i.e. cysts, will sink, become dormant and “germinate” following a
sediment upwelling allowing these germinated stages to surface again.
This laboratory exercise is designed to convey the diversity of the algae that comprise the
phytoplankton, particularly the marine phytoplankton.
I. Euglenophyta – a small phylum (division) of the kingdom Protista, consisting of mostly
unicellular aquatic algae. Living in fresh and marine waters many are flagellated and therefore
motile. The outer part of the cell consists of a firm but flexible layer called a pellicle, which
cannot properly be considered a cell wall. Some euglenoids contain chloroplasts that contain the
photosynthetic pigments chlorophyll a and b, as in the phylum Chlorophyta; others are
heterotrophic and can ingest or absorb their food. Food is stored as a polysaccharide, paramylon.
Reproduction occurs by longitudinal cell division. The most characteristic genus is Euglena,
common in ponds and pools, especially when the water has been polluted by runoff from fields
or lawns on which fertilizers have been used. There are approximately 1,000 species of
euglenoids.
1. Euglena – is a common unicell found in the planktonic zone particularly of stagnant waters.
Euglena is a protist that can both eat food as animals by heterotrophy; and can photosynthesize,
like plants, by autotrophy. When acting as a heterotroph, the Euglena surrounds a particle of
food and consumes it by phagocytosis. When acting as an autotroph, the Euglena utilizes
chloroplasts, (hence green color) containing Chlorophyll a, Chlorophyll b, and some carotenoid
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pigments, to produce sugars by photosynthesis. Each chloroplast has three membranes that exist
in thylakoid stacks of three. The number and shape of chloroplasts within the euglenophyta
varies greatly due to environmental conditions and evolutionary history.
Euglena are able to move through aquatic environments by using a large flagellum for
locomotion. To observe its environment, the cell contains a red eyespot (stigma), a primitive
organelle that filters sunlight into the light-detecting, photosensitive structures at the base of the
flagellum allowing only certain wavelengths of light to hit it. This photosensitive area detects the
light that is able to be transmitted through the eyespot. When such light is detected, the Euglena
may accordingly adjust its position to enhance photosynthesis. The mobility of Euglena also
allows for hunting capability, because of this adaptation, many Euglena are considered
mixotrophs: autotrophs in sunlight and heterotrophs in the dark. Euglena also structurally lack
cell walls, but have a pellicle instead. The pellicle is made of protein bands that spiral down the
length of the Euglena and lie beneath the plasma membrane.
Reproduction is completely asexual, following intra-nuclear mitosis. As is typical of animals
rather than plants, cytoplasmic division occurs by longitudinal furrowing of the protoplasm
beginning at the anterior end of the organism (flagellum)
Euglena can survive in fresh and salt water. In low moisture conditions, a Euglena forms a
protective wall around itself and lies dormant as a spore until environmental conditions improve.
Euglena can also survive in the dark by storing paramylon granules in pyrenoid bodies within the
chloroplast.
A. Prepare a wet mount of the living Euglena cultures. Use the pipette provided to “stir”
the contents of the culture tube to ensure that the Euglena have not settled on the bottom of the
culture tube. Withdraw water using the pipette and place one water drop on a slide and carefully
cover it with a coverslip. Euglena can be quite fast in their movements, so you may have to try
several wet mounts in order to find a live specimen.
Observe the free-swimming movements of the organisms at 10x magnification. Describe their
movement, characteristic of single apically flagellate organisms.
What other euglenoid characteristics (flagellum, reservoir or ampulla, plastids, nucleus, stigma,
paramylon) can you see at this magnification.
Figure 1: Euglena with labeled organelles in stained (left) and live (right) specimens.
B. Next, after locating several organisms in a central location. Continue to watch the movements
in and out of the field of view and try to observe the beating of the flagellum. If the movements
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are too fast use the methylcellulose solution provided. Located the following cell structures:
stigma, plastids, ampulla (see if you can find adjacent contractile vacuoles) and paramylon
bodies. Prepare a diagram of Euglena.
In an organism that is not swimming, observe the typical euglenoid movements (are there other
euglenoid movements not geared to the beating of the flagella?). Draw an outline (it is not
important to observe the internal organelles, just the pellicle) and observe the organism for about
5 minutes. Are there any changes in the shape of the organism? How are these movement
important for Euglena to adopt to life in the plankton?
Euglena is considered to be an autotroph (though it may turn heterotrophic depending on the
environment) and therefore “plant-like”. Plant cells are characterized in part by the presence of
cell walls and plastids. Why is the pellicle not considered to be a cell wall?
C. Examine the prepared (stained) slides of Euglena. Notice the single large nucleus. Can
you see a nucleolus? Carefully focusing should make the faint helically arranged lines of the
pellicle visible.
2. Phacus - oval-shaped or spherical cells, often flattened and leaf-like. Some species may be
twisted throughout the cell (Phacus helikoides) or only at the cell posterior (Phacus tortus). The
pellicle is quite rigid and is composed of wide proteinaceous strips that prevent the elastic
metabolic movements seen in Euglena and other euglenoids. The cells instead move by gliding
and swimming with their single emergent flagellum. The chloroplasts may be small and spherical
without pyrenoids, or large and discoidal with pyrenoids present. The cytoplasm of euglenoids
contains many paramylon starch storage granules, which are usually donut-shaped in Phacus
cells. Like other euglenoids, Phacus cells have contractile vacuoles and may have a redpigmented stigma to sense light.
A. Retrieve a sample of live Phacus. Prepare a wet mount and observe the live organism.
These euglenoids have a different shape compared to Euglena. In order to view the different
organelles (including the pellicle) you will have to focus through the different layers. What
organs can you observe? Make a drawing of the organism with it organelles.
Observe the organisms’ movements for five minutes. What are differences and similarities
compared to Euglena?
Figure 2: Phacus with organelles labeled.
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II. Pyrrhophyta - The division Pyrrhophyta (from the Greek "pyrrhos" meaning flame-colored,
also referred to as Dinophyceae) comprises a large number of unusual algal species of many
shapes and sizes. There are about 130 genera in this group of unicellular microorganisms, with
about 2000 living and 2000 fossil species described so far. The name "dinoflagellate" refers to
the forward- spiraling swimming motion of these organisms. They are free-swimming protists
(unicellular eukaryotic microorganisms) with two flagella, a nucleus with condensed
chromosomes, chloroplasts, mitochondria, and Golgi bodies. Biochemically, photosynthetic
species possess green pigments, chlorophylls a and c, and golden brown pigments, including
peridinin. Dinoflagellates primarily exhibit asexual cell division, some species reproduce
sexually, while others have unusual life cycles. Their nutrition varies from autotrophy
(photosynthesis; in-nearly 50% of the known species) to heterotrophy (absorption of organic
matter) to mixotrophy (autotrophic cells engulf other organisms, including other dinoflagellates).
Free-living dinoflagellates are an ancient and successful group of aquatic organisms. They have
adapted to pelagic (free-floating) and benthic (attached) habitats from arctic to tropical seas, and
to salinities ranging from freshwater, to estuaries, to hypersaline waters. Many species are found
in numerous habitats, living in the plankton or attached to sediments, sand, corals, or to
macroalgal surfaces or to other aquatic plants. Some species are present as parasites in marine
invertebrates and fish. Some even serve as symbionts, known as zooxanthellae, providing
organic carbon to their hosts: reef-building corals, sponges, clams, jellyfish, anemones and squid.
Dinoflagellates exhibit a wide variety in morphology and size (from 0.01 to 2.0 mm). They
commonly have a cell covering structure (theca) that differentiates them from other algal groups.
Cells are either armored or unarmored. Armored species have thecae divided into plates
composed of cellulose or polysaccharides, which are key features used in their identification.
The cell covering of unarmored species is comprised of a membrane complex. The theca can be
smooth and simple or laced with spines, pores and/or grooves and can be highly ornamented. In
systematics, dinoflagellates have been claimed by both botanists and zoologists. Dinoflagellates
share features common to both plants and animals: they can swim, many have cell walls, and
both photosynthetic and non-photosynthetic species are known. Botanists have grouped them
with the "microalgae" and zoologists have grouped them with the protozoa, and both have
produced classification schemes for this diverse and confusing group. Dinoflagellates have
attracted a lot of negative attention from the general public in recent times. For example, blooms
(population explosions) of dinoflagellates can cause the water to turn a reddish-brown color
known as "red tide". Red tides can have harmful effects on the surrounding sea-life and their
consumers. Additionally, certain species of dinoflagellates produce neurotoxins. These toxins are
carried up the food chain, ultimately to humans and can, sometimes result in permanent
neurological damage or even death. Yet dinoflagellates are important members of the
phytoplankton in marine and freshwater ecosystems.
1. Peridinium – Although most dinoflagellates are marine, Peridinium is a biflagellate unicell
that may live in both freshwater and marine environments. Peridinium, like many
dinoflagellates, is heterotrophic with autotrophic capabilities. Therefore, the organisms contain
many small chloroplasts, several carotenoids (responsible for the reddish-brown color) and
usually small drops of oil and starch grains alongside the chloroplasts. Like all other
dinoflagellates, Peridinium has a mesokaryotic nuclear organization, chromosomes lack histones
and remain permanently condensed. During cell division chromosomes attach to the nuclear
envelope, replicate and separate without the production of mitotic spindles. These primitive
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nuclear features are not visible unless special stains were employed.
At the light microscopy level Peridinium is most readily recognized by its “armor” (you might
think of them as fierce, armored plankters) and flagellar position. The armor, composed of
cellulosic plates, may bear various types of ornamentation. The two flagellae emerge through a
lateral pore (unlike the apical flagellum in euglenoids) with one flagellum extends as a cingulum
in a groove called the girdle surrounding the organism. The other, shorter flagellum, extends
posteriorly in a groove referred to as the sulcus. The two flagellae are both synchronized to direct
the organism’s movement with the cingular beat propelling the cell forward and the shorted
flagellum “steering” the cell. Though most dinoflagellates lack the light sensitive stigma,
Peridinium is an exception and possesses a plastid bound eyespot near the location of the
flagellar emergence. Peridinium reproduces both sexually and asexually. During sexual
reproduction the theca or armor is being discarded (similar to a molting process) after which
nuclear and cytoplasmic divisions occur. Sexual reproduction is rarely observed and involves
zygotic meiosis (What does that mean?).
A.
B.
Stained and prepared slide of Peridinium. Examine the slide carefully. Not the
position and appearance of the nucleus. View the armoring of the cell by the
cellulosic plates.
Live specimens of Peridinium to observe movement and even movement of plates
under the highest magnification.
2. Ceratium – one of the most spectacular dinoflagellates, they are covered with an armor-like
cell wall, made out of polysaccharide. The most distinguishing characteristic are the spines (also
known as horns), which increase the organisms surface: volume ration. The arms help Ceratium
float, but prevent them from moving very quickly. Another important feature is that they contain
small plasmids (minicircles). Ceratium have two flagella. These wind around the cell body. The
flagella each have different movements and shapes. The transverse flagellum beats in a spiral
motion, while the longitudinal flagellum pulses in waves. Most Ceratium species also contain
chloroplasts. Certain species are bioluminescent. Under adverse conditions, Ceratium are able to
encyst themselves as a form of protection. Ceratium are mixotrophs, obtaining food both through
photosynthesis and phagocytosis. Asexual reproduction is most common in Ceratium. However,
sexual reproduction is also possible, usually taking place under adverse conditions.
Ceratium are aquatic organisms, living in both marine and freshwater environments. They are
most common in temperate areas and are particularly common in the water of the North Sea, but
they can be found all over the world. Unlike other dinoflagellate species such as Alexandrium,
Ceratium are relatively harmless organisms. They are non-toxic, and are necessary for the food
web. However, they can cause a red tide if conditions allow for excessive blooming. While this
red tide is not toxic, it can deplete resources in its environment, causing strain on the ecosystem.
In general, though, Ceratium are necessary components of their habitats. They serve not just as
nutrients for larger organisms, but they keeps smaller organisms in check through predation.
A. Observe a prepared slide of Ceratium. Compare the armor and girdle position to those
of Peridinium.
In addition consider the function of the spines due to the increase of surface to volume ratio. In
organisms that live predominantly in temperate climates, why is the increase in surface to
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volume ratio important to survive the warm temperatures of the summer?
Figure 3: Different dinoflagellates including the armored Peridinium (left), the armored and horned Ceratium
(middle) and the unarmored Amphidinium (right).
3. Amphidinium - Small to large (<10-100 µm) unarmored free-living cell, predominantly motile,
sometimes enclosed in a hyaline cyst. Cells globular to fusiform, laterally or dorsoventrally
compressed. Epicone small and hypocone large, as the cingulum is located in the anterior part of
the cell. Some cells have larger epicones. Cingulum circular or little displaced with the cingulum
making one or a just over one turn. Sulcus extends from cingulum to antapex or posterior portion
of the organism, in some species to apex. Typical dinokaryon located in the hypocone.
Chloroplasts may be either present or absent. Nutrition is phototrophic or phagotrophic either by
ingestion of whole particles or by myzocytosis (“cellular vampirism”. Chloroplasts of some
species may be derived from cryptophycean endosymbionts. Cytoplasm is hyaline (glassy) or of
various colors, dense granules may be present. Some species form temporary cysts. Vegetative
reproduction is conducted by binary fission. Sexual reproduction known but rare. Some species
produce unusual sterols, others toxic substances. Amphidinium is cosmopolitan, marine, brackish
or freshwater, planktonic or sand-dwelling and some species may be endosymbiotic.
A. Retrieve a sample of live Amphidinium and prepare a wet mount. Notice that these
organisms are lacking the cellulosic theca and are “naked” or “unarmored”. Observe the
movement. Where are the flagellae located and how do they contribute to the overall movement
of the organism.
Can you distinguish the epicone from the hypocone? What divides these two body portions.
These organisms may be autotrophic. Can you discern the chloroplasts? Do you notice anything
unusual about the chloroplasts? Concentrate on shape, color and size.
III. Stramenopiles - Stramenopiles are a "crown" taxon that evolved about 300 million years
ago and radiated after the Cretaceous Period. They include both photosynthetic and
nonphotosynthetic taxa. Photosynthetic members include brown seaweeds, diatoms,
chrysophytes and several other groups varying in morphology from simple unicells to more
highly complex structures. These autotrophic eukaryotes impact many of the earth's
biogeochemical cycles (e.g. sulfur and nitrogen loading) and serve as primary producers that fix
a significant portion of the total CO2 processed on earth. The stramenopiles represent a major
eukaryotic group that is taxonomically distinct from the chlorophytic or rhodophytic lineages of
autotrophs.
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III.1 The Diatoms (Bacillariophyceae) - Diatoms are single-celled organisms, which secrete
intricate skeletons. Diatoms are one of the predominant autotrophic organisms, particularly in
temperate water, with approximately 10,000 species of various morphologies described. Most
taxa are unicellular and planktonic, though some may live attached to submerged vegetation and
others form colonial aggregations.
Diatom walls are composed of pectin material with large quantities of silica, the latter accounting
for about 50% of the cellular dry weight. This skeleton is divided into two parts, one of which
(the epitheca) overlaps the other (the hypotheca) like the lid of a box or petri dish. Observe the
diatom frustule below at right, in which the two halves have been pushed slightly askew. Both
epitheca and hypotheca are made up of two or more parts: the valve, a more or less flattened
plate, and at least one cingulum, a hoop-like rim. As is visible in the photographs, both parts of a
frustule may be highly perforated. Pennate diatoms show a long slit, the raphe, along the long
axis. Through the raphe, the living diatom secretes mucilage, with which it may attach to a
substrate or move by gliding over the substrate. Within their silica walls, diatoms show a typical
level of eukaryotic organization. Living diatoms contain several chloroplasts, where
photosynthesis takes place.
Diatoms may be of two body symmetries, either radial or bilaterally symmetric. Radial
symmetry genera are called centric diatoms and are always associated with marine waters while
bilateral symmetry is found in pennate diatoms, which may be found in both marine and
freshwater habitats. Many diatoms are slightly asymmetrical, though they generally fall into one
of these two categories.
A. Navicula - Cells are motile, and solitary. Cells are rectangular in girdle view, and widely
lanceolate in valve view. Both valves have a central longitudinal raphe with a nodule (bump) in
the middle. Valve surface is covered in transverse striations that are crossed by finer longitudinal
striations. Two chloroplasts are present, one on each side of the raphe. Navicula represents a
tropical, marine, benthic diatom genus.
Prepare a wet mount from the Navicula culture and scan using the 4X objective. Describe
the organisms shape. In addition investigate the differences in size of the various individuals.
Figure 4: Diatoms Navicula (left) and Thalassiosira (right).
Locate an area with several larger individuals and switch to the 40X magnification. Prepare a
sketch of the valve and girdle view of Navicula.
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Is Navicula centric or pennate in shape? What is its symmetry?
Distinguish the different thecal features, including the raphe, central nodule, central area and
striae. (If you cannot find all these features on the live specimens, use some of the prepared
slides to visualize them)
Why do you think diatoms require silica for growth?
B. Thalassiosira – This diatom genus is a marine genus, which likely descended from a
freshwater ancestor in the genus Cyclotella. Thalassiosira is solitary, or joined by threads or
valve to valve to form loose chains; or in mucilage masses. Plastids are numerous and discoid.
Mainly found in the marine plankton. The valves have a flat valve face and short down turned
mantles or sometimes almost watchglass-like. Areolae usually loculate, arranged in radial rows,
tangential rows, or arcs; varying in size and prominence. The areolae open to the outside by
circular foramina, sometimes with finger-like projections. Valve mantle edge often very
prominently ribbed and rimmed. This is a large genus with considerable variation within the
genus found in many different ocean environments.
Prepare a wet mount of the live Thalassiosira culture and observe under low
magnification. Are representatives of this genus centric or pennate? What is the size variation in
this genus compared to Navicula.
C. Chaetoceros – Chaetoceros are pelagic diatoms that build chains of varying lengths.
Occasionally the cells are solitary. The cells are constructed like a box with a lid. From above,
they are rounded, but from the side they are rectangular. Chaetoceros-diatoms always carry
outward brushes that point from the corners of the cell. In chained colonies, the brushes touch the
base of the neighboring cells. It is often possible to see two bands that run around the cells.
Compare Chaetoceros with Thalassiosira.
D. Utilize a prepared slide of diatom frustules. Observe the different varieties of sizes and forms
and prepare some drawings. Find a pennate representatives with a distinct raphe and draw the
valve and include all visible markings. Label the drawing.
E. Use the diatomaceous earth or the “Wright’s Silver Cream” and “inoculate” a drop of water
on a slide by using an needle probe and taking a small sample and swirling it around in the water.
Observe a variety of different shapes.
What are uses for diatomaceous earth?
Why would diatoms be present in silver polish?
III.2 Chrysophyceae - or golden algae, are common microscopic chromists in fresh water with
some marine species. Some species are colorless, but the vast majority are photosynthetic. As
such, they are particularly important as the primary source of food for zooplankton. They are not
considered truly autotrophic by some biologists because nearly all chrysophytes become
facultatively heterotrophic in the absence of adequate light, or in the presence of plentiful
dissolved food. When this occurs, the chrysoplast atrophies and the alga may turn predator,
feeding on bacteria or diatoms.
There are more than a thousand described species of golden algae, most of them free-swimming
and unicellular, but there are filamentous and colonial forms. Other chrysophytes may spend part
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of their life as amoeboid cells. The oldest known chrysophytes are from calcareous and siliceous
deposits of Cretaceous age, but they reached their greatest diversity in the Miocene. The group
actually has a fairly complete fossil record, because most freshwater chrysomonads secrete
resting cysts of silica, which may be abundant in certain rocks -- in some Paleocene deposits,
chrysophyte cysts outnumber the diatoms! The fossils of chrysophytes, like those of diatoms and
coccolithophorids, are often used as paleoecological indicators to reconstruct ancient
environments.
These organisms may be round, oval or somewhat heart-shaped with 2 unequal heterodynamic
flagellae (beat is not synchronized) emerging at the apical location of the organisms. Swimming
motions involve the cells pulling themselves forward by the movement of the longer flagellum.
The motion of the short flagellum allows the organism to rotate on the axis. A simple lobed
chloroplast wraps around the central part of the cell. Stigma may be present in the form of
carotenoid aggregations. A contractile vacuole is found in the flagellar zone.
A. Isochrysis – a small, unicellular, golden-brown flagellate which is of particular interest and
use in the aquaculture industry as it is cultured as a food source for developing crustacean,
bivalves and echinoderms.
Prepare a wet mount of living Isochrysis. As you are preparing the slide take note of the yellowbrown color of the culture tube. The yellow brown appearance is due to what pigments?
Observe the movements of the organisms using the 10X objective. How do their movements
compare to Euglena?
Switch to the 40X objective to study the cellular organization of the cell, particularly the
flagellae, contractile vacuole and chloroplast.
B. Nannochloropsis - genus of alga comprising approximately 6 species. The species have
mostly been known from the marine environment but also occur in fresh and brackish water. All
of the species are small, nonmotile spheres that do not express any distinct morphological
features. It is different from other related microalgae in that it lacks chlorophyll b and c.
Nannochloropsis is able to build up a high concentration of a range of pigments such as
astaxanthin, zeaxanthin and canthaxanthin. It is mainly used as an energy-rich food source for
fish larvae and rotifers. Recently, Nannachloropsis has also been investigated in terms of its
potential as source for biofuels.
Prepare a wet mount of living Nannochloropsis. As you are preparing your wet mount
notice the yellow-brown color of the culture tube. Observe the wet mount under increasing
magnifications. What is the difference between Nannachloropsis and Isochrysis? What are the
dominant pigments in both algae?
Nannochloropsis generally lack a stigma. Why would stigmata be absent in these organisms?
III.3. Xanthophyceae – or the yellow green algae, which contain chlorophyll a but lack
chlorophyll b. Instead they may possess chlorophyll e or c. Besides chlorophylls they posess
xanthophylls and beta carotene. There are about 600 species of Xanthophyceae, all but three
(Botrydium, Tribonema and Vaucheria) of the species are very rare. Before 1899 there were so
few species known that they were categorized with the Chlorophyta (green algae). They are often
confused with green algae because it is pigmented by chlorophyll and lacks the fucoxanthin that
is present in other Chyrsophyta. In fact, Xanthophyceae are "secondary endosymbionts" -- they
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evolved from protists that engulfed algae and assimilated their chloroplasts. The two main
varieties appear as large green vesicles up to several mm in diameter. Their photosynthate is
stored as oils and the storage polymer chrysolaminarin. Most Xanthophyta are coccoid or
filamentous, but some are siphonous, meaning that they are composed of multiple tubular cells
with several nuclei. What makes up the cell wall is unknown but inside some there are two silica
valves similar to those in diatoms. For the species that are filamentous the interlocking halves are
in the shape of a H. While not much is known about the life cycle of xanthophyta generally their
reproduction is asexual, in which the cell divides bilaterally and creates and produces an
endogenous cyst. Reproduction has only been observed in two xanothophtyes: in Vaucheria, it
was found to be oogamous, and Botrydium reproduces by means of bimastigote zoospores or
aplanospores. Xanthophyta are generally found in freshwater, wet soil and tree trunks, but there
are several marine species. Most of the species occur singly and are found around other algae,
making it difficult to find the same species twice. They do very well at low pH in habitats that
are rich in iron. It was also found that Xanthophyceae loses its cytoplasmic streaming ability and
organization of other vegetative filaments, when it is in an aluminum-rich environment. Many of
them are found in late winter among floating mats in still water.
A. Vaucheria - yellow-green algae characterized by multinucleate tubular branches lacking cross
walls except in association with reproductive organs or an injury. Food is stored as oil globules.
Asexual reproduction is by motile multiflagellate zoospores and nonmotile aplanospores; sexual
reproduction also occurs. The spherical female sex organ (oogonium) and the slender hookshaped male sex organ (antheridium) are usually produced on branches close to each other. After
the nonmotile egg is fertilized by a biflagellate sperm, the zygote may enter a resting phase for
several weeks before germinating into a new plant.
Examine prepared slides of Vaucheria. Distinguish between the oil globules and the chloroplasts
(you might need to go to oil resolution in order to do so).
Make a live mount of Vaucheria to determine the dominant pigmentation due to organismal
color.
Are sex organs present? If so, what kind of sex organ (male or female) is present? What are the
distinguishing characteristics and how does fertilization occur (examine the diagram below).
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