CHAPTER 11
Protozoan Groups
Unicellular
Eukaryotes
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11-2
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Emergence of Eukaryotes
Cellular Symbiosis

First evidence of life
Dates to 3.5 billion years ago
 First cells were bacteria-like
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Origin of complex eukaryote cells

Most likely symbiosis among prokaryotic cells
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Modification of engulfed prokaryote into an organelle:
Primary endosymbiosis
Aerobic bacteria engulfed by bacteria
May have become mitochondria found in most modern
eukaryotic cells
Engulfed photosynthetic bacteria evolved into
chloroplasts
Descendants in green algae lineage gave rise to
multicellular plants
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Emergence of Eukaryotes

Protozoa
Lack a cell wall
 Have at least one motile stage in life cycle
 Most ingest their food
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Other groups apparently originated by
 Secondary endosymbiosis
 One eukaryotic cell engulfed another
eukaryotic cell
 Latter became transformed into an
organelle
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Emergence of Eukaryotes

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Protozoans
 Carry on all life activities within a single
cell
 Can survive only within narrow
environmental ranges
 Very important ecologically
 At least 10,000 species of protozoa are
symbiotic in or on other plants or animals
 Relationships may be mutualistic,
commensalistic, or parasitic
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How do we define protozoan groups?
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Protozoa
 Once considered one phylum
 Recently shown that there are at least
seven or more phyla
 May be more than 60 monophyletic
eukaryotic clades
“Protozoa”
 Now used informally without implying
phyletic relationship
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How do we define protozoan groups?
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Heterotrophic protozoa obtain organic
molecules synthesized by other organisms
 Phagotrophs (holozoic feeders)
 Feed on visible particles
 Osmotrophs (saprozoic feeder)
 Feed on soluble food
Nutritional distinctions work well for
multicellular forms
 Less distinct for unicellular organisms
Mode of nutrition employed by unicellular
organisms
 Often variable and opportunistic
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11-9
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How do we define protozoan groups?

Mode of locomotion
 Used in the past to distinguish three of the
four classes of the phylum Protozoa
 Society of Protozoologists (1980)
published a new classification with seven
separate phyla
 Molecular analyses revolutionized
concepts of phylogenetic affinities in
protozoans
 May be 250,000 protozoan species
11-10
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Form and Function
Locomotion

Cilia and flagella
 Both called undulipodia
 Cilia
 Propel water parallel to the cell surface
 Flagella
 Propel water parallel to the flagellum
axis
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Form and Function
Morphologically the same
 Contain 9 pairs of microtubules arranged
around a central pair
 Arrangement called an axoneme
 Covered by plasma membrane
 Found in all motile flagella and cilia in
animal kingdom
 Kinetosome (same structure as
centioles)
 Located at base of axoneme

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11-14
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11-15
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Form and Function

Pseudopodia

Primary means of locomotion in Sarcodina, many
flagellates and ameboid cells of many invertebrates
and vertebrates
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Lobopodia
Large blunt extensions of the cell body
 Contains both endoplasm and ectoplasm
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Limax Form
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Filopodia
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Whole body moves rather than sending out arms
Thin extensions containing only ectoplasm
Reticulopodia
Repeatedly rejoin to form a netlike mesh
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Form and Function

Axopodia
Long thin pseudopodia
 Support by axial rods of microtubules
 Axoneme of the axopod
 Addition and removal of microtubular material
extends and retracts the axopod
 Cytoplasm flows away from the body on one
side and toward the body on the other

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11-20
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11-22
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11-24
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Form and Function

How Pseudopodia Work
Endoplasm
 Contains nucleus and cytoplasmic
organelles
 Ectoplasm
 More transparent (hyaline)
 Contains bases of cilia or flagella
 Often more rigid
 Appears granular
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Form and Function
A lobopodium forms by extending
ectoplasm (hyaline cap)
 Endoplasm flows into hyaline cap
 Flowing endoplasm contains actin
subunits with proteins that prevent actin
from polymerizing
 Lipids release the actin to polymerize
 Actin filaments cross-link by another actinbinding protein to form semisolid gel
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Form and Function
At the trailing edge of the gel
 Ca+ activates actin-severing protein
 Filaments are released from gel
 Myosin associates and pulls the filaments
 Contraction at trailing edge forces fluid
endoplasm back towards the hyaline cap
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Form and Function
Functional Components of Protozoan Cells

Nucleus
 Membrane bound organelle
 Contains DNA in the form of chromosomes
 Chromatin often clumps irregularly leaving
clear areas
 Imparts a vesicular appearance
 Nucleoli are often present
 Macronuclei of ciliates
 Compact or condensed with no clear areas
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11-29
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Form and Function

Mitochondria
 Involved in energy production
 In cells without mitochondria
 Hydrogenosomes may be present
 Function in absence of oxygen
 Assumed to have evolved from
mitochondria
 Kinetoplasts
 Work in association with a kinetosome
 Assumed to be mitochondrial derivatives
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Form and Function


Golgi apparatus
 Part of the secretory system of the
endoplasmic reticulum
 Parabasal bodies are similar structures
with similar functions
Plastids
 Organelles containing a variety of
photosynthetic pigments
 Perhaps added when a cyanobacterium
was engulfed but not digested
 Chloroplasts contain different types of
chlorophylls
11-31
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11-32
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Form and Function

Extrusomes
 General term applied to membrane-bound
organelles used to extrude material from
cell
 All not believed to be homologous
 Ciliate trichocysts are examples
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Form and Function
Nutrition

Holozoic nutrition implies phagocytosis
 Infolding of cell membrane surrounds food
particle
 Invagination pinches off
 Food particle contained in intracellular
vesicle
 Food vacuole (phagosome)
 Lysosomes fuse with phagosome and
release enzymes
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Form and Function
 Digested
products absorbed across
vacuole membrane
 Undigestible material released to
outside by exocytosis
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Form and Function
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
In ciliates, site of phagocytosis called a
cytostome
 Many have a point for expulsion of wastes
 Cytopyge or cytoproct
Saprozoic feeding may be by
 Pinocytosis
 Transport of solutes across cell membrane
 Diffusion is of little importance in
protozoan nutrition
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Form and Function
Excretion and Osmoregulation
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Excretion of metabolic wastes is by diffusion
Primary end product of nitrogen metabolism
 Ammonia
Contractile vacuoles fill and empty to
maintain osmotic balance
 No known lipid bilayer that retains water
against a gradient
 A proton pump may actively transport H+
ions and cotransport bicarbonate into
vacuole
 Water enters by osmosis
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11-39
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Form and Function
Reproduction

Asexual Processes
 Fission
Produces more individuals than other forms of
reproduction
 Binary fission is most common
 Two identical individuals produced
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Budding
Occurs when a small progeny cell (bud)
pinches off from parent cell
 Bud grows to adult size
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Form and Function

Multiple fission (schizogony)
Cytokinesis preceded by several nuclear
divisions
 May individuals formed simultaneously
 If union of gametes precedes multiple fission
 Called sporogony
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Form and Function

All of above accompanied by some form of
mitosis
 Mitosis in protozoa divisions varies from
metazoan mitosis
Nuclear membrane often persists
 Spindle may form within the nuclear membrane
 Centrioles not observed in ciliates
 Macronucleus of ciliates elongates, constricts,
and divides without mitosis (amitosis)

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Form and Function

Sexual Processes
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All protozoa reproduce asexually
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Sexual reproduction also occurs widely
among protozoa
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May precede phases of asexual reproduction
Isogametes
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Some exclusively
Gametes look alike
Anisogametes
Gametes are dissimilar
 Characteristic of most species
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Form and Function

Meiosis
 May occur during or just before gamete
formation
 In other groups, meiosis occurs after
fertilization (zygotic meiosis)
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All individuals produced asexually in life
cycle up to next zygote are haploid
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Form and Function
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
Fertilization of one gamete by another
 Syngamy
Some sexual phenomena do not involve syngamy
 Autogamy
 Gamete nuclei form by meiosis
 Fuse to form a zygote inside the parent
organism
 Conjugation
 Gamete nuclei exchanged between paired
organisms
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Form and Function
Encystment and Excystment
 Unicellular forms amazingly successful in
extremely harsh conditions
 Related to the ability to form cysts
 Dormant forms that shut down
metabolism and have a resistant
external covering (secreted by Golgi
apparatus)
 Encystment is not found in Paramecium,
rare or absent in marine forms
 Excystment
 Escape from cysts when environmental
conditions are favorable
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
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Major Protozoan Taxa
Clade Stramenophiles
Tubular mitochondrial cristae
 Heterokont flagellates
 Two different flagella, both inserted in
the anterior end
 Includes plant-like brown algae, yellow
algae, and diatoms
 Also contains opalinids, a group of animal
parasites
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Major Protozoan Taxa
Clade Opisthokonta
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Flattened mitochondrial cristae
Posterior flagellum on flagellated cells, if such
cells exist
Metazoans, fungi, and some unicellular taxa
previously considered protozoans
Best known in this group are microsporidians and
choanoflagellates
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11-50
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Major Protozoan Taxa
Clade Viridiplantae
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Unicellular and multicellular green algae,
bryophytes, and vascular plants
 Phylum Chlorophyta
 Flagellated, autotrophic, single-celled
algae such as Chlamydomonas, as
well as colonial forms like Gonium
and Volvox
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Major Protozoan Taxa
 Mode
of development of Volvox is
similar to embryonic development of
some metazoans
 Hollow ball of cells, reminiscent of
metazoan blastula
 Suggested that first metazoan was
nonphotosynthetic flagellate similar in
design to Volvox
 Each organism contains thousands of
cells
 Cells resembles a euglenid:
Nucleus, pair of flagella, large
chloroplast, and stigma
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Major Protozoan Taxa
 Cytoplasmic
strands connect cells
 Stigma are larger at one pole
 Most cells are somatic concerned with
nutrition and locomotion
 Few germ cells function in
reproduction
 Reproduction: sexual or asexual
 Asexual
Reproduction
 Repeated
mitotic division form
daughter colonies
 Formed inside parent colony
 Rupture through wall to escape
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Major Protozoan Taxa
 Sexual
 Cells
Reproduction
differentiate into
macrogametes and microgametes
 Macrogametes
Larger, fewer, and store food for
nourishment of young organisms
 Microgametes
Smaller and form bundles of
flagellated sperm that swim freely
until they find an ovum
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Major Protozoan Taxa
 Zygote
 Secretes
a hard, spiny, protective
shell and overwinters
 In spring, repeated divisions allow
it to break out
 Asexual reproduction occur in the
summer
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11-56
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Major Protozoan Taxa
Phylum Euglenozoa
Generally considered as monophyletic
 Have a series of longitudinal microtubules
 Stiffen the cell membrane into a pellicle
 Subphylum Euglenida
 Chloroplasts surrounded by a
double membrane

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Major Protozoan Taxa
 Euglena
viridis
 Freshwater with abundant
vegetation
 Flagellum extends anterior end
 Kinetosome located at the base of
the flagellum
 Oval chloroplasts
 Stigma functions in orientation to
light
 Normally autotrophic, but can
make use of saprozoic nutrition
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Major Protozoan Taxa
Subphylum Kinetoplasta
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Zooflagellates
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Lack chromoplasts
Holozoic or saprozoic nutrition
Most are symbiotic
Trypanosoma
 Important genus of protozoan parasites
 Some not pathogenic
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Major Protozoan Taxa
 T.
brucei gambiense and T. b.
rhodesiense

 T.

 T.
Cause African sleeping sickness in
humans
brucei brucei
Causes a related disease in domestic
animals
cruzi
Causes Chagas disease
 All 3 transmitted by tsetse flies
 Transmitted by “kissing bugs”

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Major Protozoan Taxa

Phyla Retortamonada and Diplomonads
 Divided into 2 clades:
Retortamonds and Diplomonads
 Retortamonds
Include commensal and parasitic unicells
 Lack mitochondria and Golgi bodies
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
Diplomonads
Lack mitochondria
 Mitochondrial genes are present in the cell
nucleus
 Absence of mitochondria may be a
secondary derivation
 Giardia live in the digestive tract of humans,
birds, and amphibians

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Major Protozoan Taxa
Clade Alveolata
Three traditional phyla united by the
shared presence of alveoli
 Membrane-bound sacs beneath cell
membrane
 Function varies with phylum
 Phylum Ciliophora
 Phylum Dinoflagellata
 Phylum Apicomplexa

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Major Protozoan Taxa
Phylum Ciliophora
Ciliates are the most diverse and
specialized protozoans
 Larger than most other protozoa
 Most free-living, some commensal and
parasitic
 Usually solitaire and motile
 Most free-living in freshwater or marine
habitats

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Major Protozoan Taxa

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Multinucleate
 At least one macronucleus and a
micronucleus
 Macronuclei
 Metabolic and developmental
functions
 Divides amitotically
 Micronuclei
 Involved in sexual reproduction and
give rise to macronuclei afterwards
 Divide mitotically
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Major Protozoan Taxa
Pellicle varies from a simple membrane to
thickened armor
 Cilia
 Arranged in rows
 Propel food to the cytopharynx
 Fused cilia (cirri) used in locomotion
 Most are holozoic

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Major Protozoan Taxa
 Suctorians
 Ciliates
that paralyze their prey and
 Ingest contents through tube-like
tentacles
 Trichocysts and toxicysts in some
 Expel long thread-like structures
when stimulated
 Believed to be defensive mechanism
 Other
common ciliates
 Stentor,
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Vorticella, and Euplotes
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Major Protozoan Taxa
 Symbiotic
Ciliates
 Balantidium
coli lives in the intestine of
humans, pigs, rats,
 Not usually pathogenic
 Entodinium and Nyctotherus live in
tracts of ruminants and frogs and toads,
respectively
 Ichthyophirius causes the fish disease
“ick”
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11-72
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Major Protozoan Taxa
 Free-living
ciliates
 Stentor
 Trumpet
shaped and solitary
 Bead-like macronucleus
 Vorticella
 Bell shaped
 Attached by a contractile stalk
 Euplotes
 Flattened body
 Groups of fused cilia
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Major Protozoan Taxa
 Paramecium
may be studied as a typical
free-living ciliate
 Slipper-shaped
 Asymmetrical appearance caused by
oral groove
 Pellicle may be ornamented, have
ridges, or papillalike projections
 Trichocysts present
 Cytostome leads to a tubular
cytopharynx
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Major Protozoan Taxa
 Fecal
material discharged from the
cytoproct
 2 contractile vacuoles
 Kidney-shaped macronucleus with
smaller micronucleus alongside
 Some species have up to seven
micronuclei
 Holozoic
 Body is elastic
 Can bend and squeeze through
spaces
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Major Protozoan Taxa
 Cilia
can beat forward, backward or
obliquely
 Taxic movements orient it to stimuli
 Kineses merely slow or speed up
movement
 Reproduction
Binary fission
 Conjugation
 Autogamy
 Self-fertilization similar to conjugation
but no exchange of nuclei

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Major Protozoan Taxa
Phylum Dinoflagellata
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About half are photoautotrophic
Chloroplasts possibly acquired by endosymbiosis
Some among the most important primary producers
in marine environments
Commonly have two flagella
Body naked or covered by cellulose plates
Many have a mouth region through which they can
ingest prey
Many are bioluminescent
Zooxanthellae
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
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Live in mutualistic association with corals and other
invertebrates
Only corals with symbiotic zooxanthellae form coral reefs
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Major Protozoan Taxa
Phylum Apicomplexa

Endoparasites
 Hosts are in many animal phyla
 An apical complex is a feature of this
phylum
 Present only in certain stages
 Rhoptries and micronemes aid in
penetrating host’s cells
 Pseudopodia occur in some stages
 Gametes may be flagellated
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Major Protozoan Taxa


The life cycle usually includes both sexual
and asexual stages
 Invertebrate may be an intermediate host
During life cycle
 Form a spore (oocyst)
 Infective in the next host
 Protected by a resistant coat
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11-84
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Major Protozoan Taxa
 Class
Coccidea
 Intracellular
parasites in invertebrates
and vertebrates
 Include species of great medical and
veterinary importance
 Eimeria is a genus (along with
Isospora) that causes coccidiosis
 Isospora infections are mild unless
the immune system is weak, as in
AIDS patients
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Major Protozoan Taxa
 Eimeria
 Often
tenela
fatal to young fowl
 Organisms undergo schizogony in
intestinal cells
 Zygote forms an oocyst that exits
via the feces
 Releases eight sporozoites when
ingested by the next host
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Major Protozoan Taxa
 Toxoplasma
 Parasite
gondii
of cats
 Rodents, cattle, sheep, birds and humans
can ingest sporozoites
 Cross the intestine and asexually
reproduce in tissues
 Zoites enclose in tissue cysts called
bradyzoites
 Up to ½ of the U.S. population carries
cysts from eating undercooked meat
 Serious threat during pregnancy; 2% of
the cases of mental retardation may be
due to congenital toxoplasmosis
11-87
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11-88
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Major Protozoan Taxa
 Plasmodium:
 Most
The Malarial Organism
important infectious disease of
humans
 Four species infect humans
 Each produces different clinical
symptoms
 Anopheles mosquitoes carry all forms
 Female injects the Plasmodium
present in her saliva
 Sporozoites penetrate liver cells and
initiate schizogony
11-89
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Major Protozoan Taxa
 Products
of this stage penetrate
more liver cells
 In P. falciparum they penetrates
red blood cells after only 1 cycle
 Incubation period in liver is 6–15
days
 Liver releases merozoites
 Enter red blood cells where they
begin schizogonous cycles
 Now called ameboid trophozoites
11-90
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Major Protozoan Taxa
 Feed
on hemoglobin
 Digest hemoglobin into hemozoin
 Hemozoin released as the next
generation of merozoites is
produced and accumulates in the
liver, spleen, and other organs
11-91
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Major Protozoan Taxa
 Cyclic
release of foreign
substances produces the chills
and fever of malaria
 Plasmodium vivax (benign tertian)
and P. ovalae: every 48 hours
 P. malariae (quartan): every 72
hours
 P. falciparum (malignant tertian):
about every 48 hours
 P. falciparum is the most common
(50%) and the most fatal, leading to
cerebral malaria
11-92
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Major Protozoan Taxa
 After
cycles of schizogony,
merozoites produce
microgametocytes and
macrogametocytes
 Gametocytes in blood ingested by
mosquitoes
 Mature into gametes in insect gut
and fertilization occurs
 Zygote becomes a motile ookinete
 Penetrates the stomach wall of the
mosquito and becomes an oocyst
 Oocyst undergoes sporogony and
thousands of sporozoites are
produced
11-93
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Major Protozoan Taxa
 Migrate
to the mosquito’s salivary
gland where they are injected into a
human host
 Development in the mosquito may
take 7–18 days
 Elimination of mosquitoes and
breeding places is difficult
 Insecticide resistance by
mosquitoes and drug resistance by
Plasmodium contributes to the
problem
 Culex mosquitoes transmit bird
malaria
11-94
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Major Protozoan Taxa

Parabasalids
 Parabasalid clade
Contains some members of the phylum
Axostylata
 Individuals possess a stiffening rod
composed of microtubules: axostyle
 Parasbasalids have a parabasal body



11-95
Modified region of the Golgi apparatus
Much of the work on parabasalid structure has
been done on species of Trichomonas
 Trichomonas vaginalis
 Infects the urogenital tract of humans
 Sexually transmitted
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11-96
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Major Protozoan Taxa

Amebas
Found in fresh and salt water, and moist
soils
 Some planktonic, some require a
substratum
 Most reproduce by binary fission
 Sporulation and budding are also seen
 Nutrition is holozoic

11-97
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Major Protozoan Taxa
 Non-actinopod
 May
amebas
form lobopodia, filopodia, or
rhizopodia
 Rhizopodia are seen in Amoeba proteus,
the most commonly studied ameba
 Slow streams and ponds of clear water
 Require a substratum
11-98
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Major Protozoan Taxa

Entamoebidae
Members of clade Lobosa
 Branched pseudopodia make them
rhizopod amebas
 Lack mitochondria
 Entamoeba histolytica most important
rhizopodan parasite of humans
 Lives in the large intestine
 Invade the intestinal wall by secreting
enzymes that attack the intestinal lining
 Can lead to amebic dysentery

11-99
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Major Protozoan Taxa

Granuloreticulosa
Slender pseudopodia extending through
openings in test
 Most are foraminiferans
 Ancient group of shelled amebas found
in all oceans
 Most live on the ocean floor
 Perhaps largest biomass of any animal
group
 Most tests are many-chambered and
made of calcium carbonate

11-100
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11-101
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Major Protozoan Taxa
 Complex
life cycles, with multiple
fission and alternation of haploid and
diploid generations
 Foraminiferans have existed since
Precambrian times
 Well documented in record
 Some among largest protozoa that ever
lived (100 mm diameter)
 About 1/3 of sea bottom is covered with
foraminiferous ooze
11-102
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Major Protozoan Taxa
 Limestone
and chalk deposits have
been laid down by foraminiferan
accumulations
 Chalk deposits of many areas of
England, including White Cliffs of Dover,
formed in this way.
 Fossil foraminiferan identification is
often important to oil geologists for
identifying rock strata
11-103
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Major Protozoan Taxa

Actinopod Amebas
Polyphyletic group with axopod
pseudopodia
 Descriptive names radiolaria and heliozoa
applied to some.
 Helizoan refers to freshwater ameba with
or without tests, such as Actinosphaerium

11-104
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Major Protozoan Taxa
 Radiolarian
 Refers
to marine testate ameba with
intricate skeletons
 Oldest known protozoa
 Pelagic and live in shallow water
 Shell surface fused with spines
 Cytoplasm around the capsule extends
axopodia to catch prey
 Reproduce by binary fission,
budding,and sporulation
 Useful for determining the age of rock
strata
11-105
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11-106
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Phylogeny and Adaptive Diversification

Phylogeny

Molecular evidence has greatly changed
phylogeny of unicellular eukaryotes
Ancestral eukaryote diversified into many
morphologically distinct clades
Assumed that all amitochondriate
protozoans had ancestors with mitochondria
Plastids were transferred among eukaryotic
lineages by primary, secondary and tertiary
endosymbiotic events



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Phylogeny and Adaptive Diversification




Explains why particular plastids are found
among a wide variety of seemingly unrelated
single and multicellular eukaryotes
Using molecular data sets and the pathway
of endosymbiont transfers, eukaryotic
lineages combined into a few eukaryotic
supergroups
Two supergroups not shown in Figure 11.1
created by combining different taxa
Viridiplantae combined with red algal clade
and glaucophytes to form supergroup
Plantae
11-108
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Phylogeny and Adaptive Diversification


Granuloreticulosans are joined with
radiolarians and cercozoans in the
supergroup Rhizaria
There is weak support for a fifth supergroup,
Excavates, whose members share an
unusual feeding groove.
11-109
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Phylogeny and Adaptive Diversification

Adaptive Diversification

Ameboid forms
Have radiated into a wide range of
environments
 Have become morphologically diverse


Flagellated forms
Have adapted to a wide range of habitats and
 Show great variation


Specialization

11-110
Most advanced in ciliates and intracellular
parasites in Apicomplexa and Microspora
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Phylogeny and Adaptive Diversification
Classification
Phylum Chlorophyta
Phylum Retortamonada
Class Diplomonadea
Order Diplomonadida
Phylum Axostylata
Class Parabasalea
Order Trichomonadida
Phylum Euglenozoa
Subphylum Euglenida
Class Euglenoidea
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Subphylum Kinetoplasta
Class Trypanosomatidea
Phylum Apicomplexa
Class Gregarinea
Class Coccidea
Phylum Ciliophora
Phylum Dinoflagellata
Amebas
Rhizopodans
Granuloreticulosans
Actinopodans