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
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
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
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
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INVERTEBRATE
ZOOLOGY
BIOLOGY 320
FALL 2005
Chapter 2
Introduction to Protozoa
Background Information

Domain Eukarya
– Membrane bound organelles,
including nucleus



Many kingdoms, 40+,
depending on what
classification scheme is
used
Classification is always
changing
Protozoa are animal-like
protists

Primitive
– Single celled
– Colonial


Gave rise to modern day
plants and animals
Diversity is the rule in
every aspect
–
–
–
–
Feeding / energetics
Life cycles
Reproduction
Physiology /
osmoregulation
– Locomotion
– Morphology
Protozoan Diversity
Review of the Eukaryotic Cell

Protists lack cellular specialization (with few exceptions)

Individual organelles carry out all physiological processes

Cell membrane
– Barrier to the outside environment
– Selective passage of molecules
– Plays a role in endo / exocytosis

Cytoplasm
– Ectoplasm – outer, stiff, portion
– Endoplasm – inner, fluid, portion

Internal membrane system
– Consists of endoplasmic reticulum (ER), Golgi
bodies, and lysosomes
– Compartmentalizes the cell
The Cytoskeleton

Main types
– Microfilaments
(made of Actin)
– Microtubules

Functions
– Maintain cell shape
– Locomotion – cilia,
flagella, and
pseudopodia
– Cell division
– Transport vesicles
around cell
Cilia


Numerous, short
projections that beat in an
oar-like fashion to produce
movement
Consists of microtubule
core (axoneme) enclosed
in cell membrane
– Ring of 9 doublets, plus two
singlets, centrally located
– (9x2)+2 pattern

Anchored by a basal body
(9x3 pattern)
Flagella




Far fewer than cilia,
but structurally
identical
Long
Undulate in a whiplike fashion to produce
movement
Both cilia and flagella
require ATP to move
Pseudopodia


Used for locomotion, food capture, and endocytosis
Actin disassembly results in a conversion of ectoplasm to
endoplasm
Protozoan Physiology

Same rules apply in single celled organisms as do
in metazoans

In fact, environmental effects may be more
pronounced
– Ectothermic
– Large SA : Vol

Important considerations
–
–
–
–
Feeding and nutrition
Enzyme function
Osmoregulation
Reproduction
Feeding and Nutrition

Heterotrophs

Photoautotrophs

Mixotrophs
– Can switch between
heterotrophy and
autotrophy, depending
on conditions

Endosymbiotic theory
explains how energy
producing organelles
evolved

Nutrition occurs in
four phases:
– Ingestion
– Digestion –mechanical
and/or chemical
– Absorption
– Elimination

Digestion typically
intracellular. Food is
phagocytized and a
food vacuole is
created. Digestive
enzymes are dumped
into vacuole
Enzyme Function


Protein form equals
function
Enzymes are subject
to denaturation under
the following
conditions:
– Extreme pH
– Extreme temperature
(especially high
temperatures)
– Extreme salinity. For
this reason,
osmoregulation is
important
Osmoregulation



Many protists posses a specialized
organelle known as a contractile vacuole
A collection of tubules known as the
spongiome, collect ions from the
cytoplasm and deliver them to the
contractile vacuole proper
The vacuole contracts and its contents
are extruded
 The
consequences of being an
osmoconformer
Reproduction

All species reproduce
asexually (clonally)
– Fission – splitting of
parent that results in two
or multiple individuals
– Budding – portion of
parent splits off to form
new individual

No recombination
Budding Hydra (NOT a Protozoan)


Though less common
some species can
even reproduce
sexually
Conjugation
– two individuals fuse
– dissolve portions of
their cell membranes
– exchange genetic
material

Recombination is the
result
Asexual vs. Sexual

Advantages to clonal reproduction
– Allows reproduction in the absence of a mate. Good for
isolated species
– Allows offspring to be reproduced quickly; no energy is
lost to gamete production, fertilization, or development
– Perpetuates identical genotypes; beneficial if already
well adapted to that environment

Disadvantage
– Limited genetic possibilities. Constricts the gene pool
and species could die out when the environment
changes

Advantages to sexual reproduction
– Increases genetic variability via crossing
over, independent assortment of
chromosomes, and random fertilization
– Result may be better environmental
adaptability for certain individuals, and the
species as a whole

Disadvantage
– Finding mates in isolated or sessile species
Encystment
 Water
is pumped out and organism
forms capsule around itself
 Benefit
is the organism can survive
harsh environmental conditions for
years
– Desiccation resistant
– Does not require food
– Wind dispersal
INVERTEBRATE
ZOOLOGY
BIOLOGY 320
FALL 2005
Chapter 3 - Protozoa
Protozoa



Name means “first
animals”
215,000 described
species. Equal to the
number of described
vascular plants
10 times more diverse
than bacteria and
viruses
Protozoan Ecology

Very important ecologically

Many are photoautotrophs, and make up 40% of
all primary productivity

Many make up a large component of plankton
communities

25% of the described species live as symbionts.
Many of these are parasitic

Many are important nutrient cyclers
Form and Function


Protozoan body was is
known as a pellicle
Pellicle is composed of
the cell membrane
and cytoskeleton:
–
–
–
–
Microfilaments (Actin)
Microtubules
Vesicles such as alveoli
Any combination of the
above
Phylum Euglenozoa

Two main classes
– Euglenoidea
– Kinetoplastida



Both are flagellates
Both reproduce
asexually
Both are solitary
Class Euglenoidea

1000 species

Elongate

Free-living

Solitary

Reproduction is
clonal, and
occurs via
longitudinal
binary fission

Posses a contractile vacuole

Two flagella, one long, one short

Posses a pigmented eyespot that shades the
photosensitive paraflagellar body

Heterotrophic, photoautotrophic, or mixotrophic

Photosynthetic species rotate on their
longitudinal access as they swim toward the light

Can produce a starch-like carbohydrate
– Known as paramylon
– Produced in the pyrenoids of their chloroplasts
– Stored as granules in cytoplasm
Class Kinetoplastida

600 species

Reproduce asexually

Posses one or two flagella

Most are parasitic

All posses a conspicuous
mass of DNA, known as a
kinetoplast, located in
one large mitochondrion

Link between
kinetoplast and
parasitic lifestyle of
most species
– Kinetoplast codes for
mitochondrial
morphogenesis
– Parasites alternate
between aerobic and
anaerobic host
environments

Trypanosoma is a gut
parasite of insects and
blood parasite of
vertebrates
– Chagas’s disease
– African sleeping sickness
Tsetse Fly Distribution
 Trypanosoma
possesses one large
flagellum that joins an undulating
membrane, which runs the length of
the organism
 The
pellicle’s protein composition
(antigens) is controlled by roughly
1000 genes (40% of the genome)
– Thus, the parasite is able to effectively
elude the host’s immune system
Phylum Chlorophyta




Green algae
Posses chloroplasts
with chlorophyll a and
b (same as plants)
Can synthesize and
store starch
Marine and freshwater
species




Some genera are non-motile and
filamentous, such as Spirogyra
Others such as Volvox are flagellated,
motile, and colonial
In Volvox, up to 6000 individual cells may
make up a hollow spherical colony
Individual cells are connected by
cytoplasmic bridges

There is some cellular differentiation in
Volvox
– Non-flagellated gonidia (reproductive cells) can
reproduce sexually or asexually

During asexual reproduction:
– Gonidium undergoes several rounds of fission
– Inverted (flagella pointing in) daughter colony
is created
– Flagella later point out
– Daughter colony bursts out of the parent
colony

Volvox is closely related to plants, but also
provides insight to the evolution of
animals
– Blastocysts look almost identical
Phylum Choanoflagellata

600 species

Marine and freshwater

Tiny - 10µm

Solitary or colonial

Free-living or sessile

Stalked, spherical, or
occurring in sheets

Not surprising that they are
closely related to animals
– Closely resemble collar cells of
sponges




One large flagellum w/ base
surrounded by a collar of
microvilli
Flagellum beats and collar
traps bacteria and organic
molecules
Particles ingested by
phagocytosis
Intracellular digestion
Phylum Retortamonada

Often live in anoxic
environments
– Many living in the guts of
insects and vertebrates
– Mitochondria typically
absent, as a result of this
– Thus, adapted for
surviving on glycolysis


Giardia lamblia posses four
flagella
Giardia is often contracted
by drinking from mountain
streams. Symptoms are
often referred to as
“beaver fever.”
Phylum Axostylata



Another heterotrophic
flagellate, closely related
to the members of
Phylum Retortamonada
Trichomonas vaginalis is
the most famous
representative
Small parasite with four
flagella that infects the
urogenital tract of
humans
– Can be transmitted
sexually
Phylum Alveolata
 Consists
of three subphyla:
– Dinoflagellata
– Ciliophora
– Apicomplexa
 Have
similar rDNA sequences
 Posses
alveoli, sacs, deep to the cell
membrane
Subphylum Dinoflagellata

Dinoflagellates

4000 marine and
freshwater species

Posses chloroplasts
– Important 1° producers
– Red-brown to gold-brown
in color, due to
photosynthetic pigments
– Chloroplasts acquired
through endosymbiosis

Contribute to planktonic
bioluminescence


Some are endoparasites of protozoa,
crustaceans, and fish
Certain genera responsible for “red tides.”
– May result in massive die-offs of shellfish and fish
– Harms animals who eat contaminated organisms



Posses a sulcus
and two flagella
Have a skeleton
known as a theca
(test or lorica)
Reproduce via
binary fission, or
may encyst
Subphylum Ciliophora

8000 described ciliates

Sophisticated protozoans

Have some degree of anterior – posterior
polarity

Most are motile and solitary

Many posses specialized ciliature
– Somatic cilia
– Oral cilia


Function of alveoli is to
store Ca2+
Release of Ca2+ causes
changes in ciliary beat,
and discharge of
extrusomes
– Trichocysts – long shafts
that are thought to defend
against predators
– Toxicysts – longs shafts with
toxin that are used for prey
capture
– Mucocysts – release mucus
and creates sticky surface
for prey capture or
protective cysts

Paramecium changes
directions upon
colliding with
something solid
– Known as avoidance
reaction
– Result of Ca2+ and K+
release from alveoli
– Depolarization, similar
to an action potential

Two very interesting
sessile genera,
Vorticella and Stentor

Vorticella
– Colonial
– Each cell possesses
a long stalk with a
spasmoneme (spiral
fiber)
– Contracts to
withdraw from
predators

Stentor is a similar
genus

Ciliates have two types of nuclei
– Macronucleus – genes are actively transcribed
– Micronucleus – master copy of genome; inactive except
during cell division

Shapes and numbers of these nuclei varies across
genera
– Bean shaped in Paramecium
– String of beads in Stentor
Subphylum Apicomplexa




Another group of
alveolates
The sporozoans, form
spores
Mostly parasitic
Posses an apical
complex
– Attaches to or
penetrates host cell
– Cone contains digestive
enzymes

Four species of Plasmodium that cause malaria
– #1 human parasite
– 300 million worldwide infected each year
– 1% die each year
– Anopheles mosquito is the vector

Complex life cycle
– Sporozoite – motile, infective stage possessing apical complex
– Merozoite – motile, reinfective stage, also has apical complex
– Gametocytes – reproductive stage. Usually, male and female
gametocytes pair up and release gametes (sexual
reproduction)
– Spore – gametes pair to form zygotes, and a protective
capsule is secreted

Sporozoites
– Injected into blood by
mosquito
– Attack liver cells

Merozoites
– Derived from sporozoites
– Reinfect liver cells or move to
red blood cells (RBCs)
– Reinfect RBCs, in pulses

Cyclical merozoite release
correlates with cyclical
nature of malaria
symptoms
– Chills
– Fever
– Fatigue due to loss of
hemoglobin
– Serious damage due to the
blocking of capillaries by
infected (less pliable) RBCs

Gametocytes
– Formed in RBCs, but do
not pair
– Release gametes in the
gut lumen of mosquito,
after being ingested
– Form zygotes which
penetrate gut wall and
encyst to form spore
– Sporozoites, produced in
spore, later migrate to
salivary glands
– Sporozoites released with
mosquito’s next blood
meal
Amoeboid Protozoa

Posses pseudopodia for locomotion and prey capture
(heterotrophs)

Have a complex cytoskeleton

Marine, freshwater, and terrestrial species

Same design found elsewhere in the animal kingdom
– Archeocytes of sponges
– Mammalian white blood cells (WBCs)

Three main groups of amoeboid protozoans
– Amebas – 3 Phyla
– Phylum Foraminifera
– Phylum Actinopoda
Amebas

Several important genera
that you will study in lab
–
–
–
–
–



Amoeba
Chaos
Entamoeba
Arcella
Difflugia
May or may not have a
test (lorica, theca)
Arcella has dome shaped
test covering its top;
pseudopodia extend from
underneath
Chaos can reach 5mm in
length

Diversity of
pseudopodia
– Lobopodia – wide and
rounded
– Filopodia – slender and
may be branched

Freshwater species
have one to several
contractile vacuoles
– No need in marine
species

Some like Entomoeba
histolytica are
parasitic
– Causes dysentery
Phylum Foraminifera

The forams

Mostly marine


Numerous
reticulopodia (special
filopodia) branch and
interconnect to form
reticulopodial network
Vesicular traffic gives
reticulopods a
granular appearance

Locomotion is
accomplished by
reticulopodial network
– Extends
– Anchors to substrate
– Retracts



Forms a probing net that
is also used for finding
food
Have a test, usually
composed of calcium
carbonate
Most are
multichambered.
Usually start life
occupying one chamber,
but extend and secrete
new tests

May be benthic or
planktonic, and there
are structural
differences between
the tests of the two
types
– Planktonic tests are
more fragile
– Also have spines to
increase surface area,
and thus buoyancy

Foram tests create
natural wonders in the
form of chalk and
limestone
– Pink sands of Bermuda
– White Cliffs of Dover in
England
– Blocks of pyramids
Phylum Actinopoda

Planktonic

Spherical with a
perforated test

Posses many axopodia
– Long, stiff, needle-like
pseudopodia
– Have microtubule support
rods
– Can attach and retract
– Used for flotation,
locomotion, and hunting
 Distinct
cellular regions due to the
presence of a layer of pseudopodia
(not actinopods)
– Cortex – shroud of pseudopodia over the test.
Digests prey and transfers nutrients
– Medulla – inner portion of cell. Houses
nucleus, nutrients, or oil drops for buoyancy
 Divided
into two classes
– Radiolaria
– Heliozoa
Class Radiolaria

Marine

Mostly planktonic


Siliceous, spherical
test
Large, up to 20cm
in some colonial
species
Class Heliozoa




Sun animalcules
Marine, freshwater, or
terrestrial (on
mosses)
Contractile vacuoles in
freshwater species
Similar to radiolarians