BIOL 201: Invertebrate Zoology

Chapter 3: Protozoa

Rob SwatskiAsst. Prof. Biology

HACC-York1

Protozoa

“First animals”

215,000 described species (equal to the # of described plants)

Incredibly diverse!

Major ecological value

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Protozoan Ecology

Many are important nutrient cyclers

Many photoautotrophic, & make up 40% of all primary productivity

Major component of plankton communities

25% of the described species live as

symbionts; many parasitic

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Protozoan Structure &

FunctionPellicle: protozoan

body wall (cell membrane & cytoskeleton)

Cytostome: cell mouth where food enters a vacuole via

phagocytosis

Test (lorica, theca, shell): internal or external skeleton

Alveoli: vesicles below cell membrane

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Osmoregulation

Hypotonic & hypertonic

environments create osmotic problems

for organisms

Osmoregulation = the control of water

balance

Contractile vacuoles

Contractile Vacuoles

Network of vesicles or tubules (spongiome), that collect ions from

cytoplasm

Ions delivered to the contractile vacuole

Vacuole contracts & its contents are expelled

Rate of discharge varies: every 6 sec to 15

min6

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Contractile Vacuoles

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Hypotonic solution

Lysis Normal

Isotonic solution

Shriveled

Hypertonic solution

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Tonicity

Asexual (Clonal)

Reproduction

Most protozoa reproduce asexually via mitosis

Binary Fission: splitting of parent into 2 similar

daughter cells

Budding: portion of parent splits off to form a new

smaller individual

Nuclear membrane stays intact & spindle forms inside

(closed spindle)11

Sexual Reproduction

Widespread, but not universal

Conjugation: fusion of 2 individual cells

DNA

Areas of cell membranes dissolve & genes exchanged

Very diverse & complex life cycles

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Asexual Reproduction: Pros/Cons

PRO: Reproduction

can occur without a mate

(good for isolated species)

PRO: Produces offspring

quickly; no energy wasted

in gamete production,

fertilization, or development

PRO: Continues identical

genotypes (beneficial if already well-

adapted to that environment)

CON: Limited genetic

possibilities; constricts gene pool & species could die out if environment

changes

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Sexual Reproduction: Pros/Cons

PRO: Increases genetic variability via

crossing over, independent

assortment, & random fertilization

PRO: May improve environmental adaptability for

certain individuals & the entire species

CON: Finding mates in isolated or sessile

species

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Encystment

Found in most FW species: pumps water

out of cell & surrounds itself with a cyst

Can survive harsh environmental

conditions for years

Resists desiccation & does not need food

Water, wind, & mud dispersal

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Phylum Euglenozoa

Two main classes: Euglenoidea & Kinetoplastida

Flagellates

Solitary & free-living

Reproduce asexually

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Class Euglenoidea

(Phylum Euglenozoa)

1000 species

Two flagella: 1 long & 1 short

Euglenoidmovement: peristaltic

motion

Asexual reproduction occurs via longitudinal

binary fission17

Class Euglenoidea,

cont.

Contractile vacuole

Pigmented eyespot shades a photosensitive paraflagellar

body

Heterotrophic, photoautotrophic, or

mixotrophic

Photosynthetic species rotate on their longitudinal axis as

they swim toward light

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Euglenoids 19

Class Kinetoplastida

(Phylum Euglenozoa)

600 species; most parasitic

Elongate cells with 1-2 flagella & undulating

membrane

Asexual reproduction

All contain a mass of DNA (the kinetoplast),

located in a large mitochondrion

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Kinetoplast

Link between kinetoplast &

parasitic lifestyle

Codes for mitochondrial

morphogenesis

Parasites alternate between aerobic &

anaerobic host environments

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Trypanosomes(Class

Kinetoplastida)

Parasite causing African sleeping sickness, transmitted by tsetse

fly

One large flagellum joining an undulating membrane, which

runs the length of the cell

Pellicle’s protein composition (antigens) controlled by roughly

1000 genes (40% of genome)

Invades CSF & brain, causing lethargy, drowsiness, & mental

deterioration22

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Phylum Chlorophyta

Marine & FW green algae

Large, cup-like chloroplasts with chlorophylls a & b (same as plants)

Synthesize & store starch

Diverse nonmotile(filamentous) &

motile forms24

Phylum Chlorophyta,

cont.

Motile solitary flagellates

(Chlamydomonas)

Motile colonial flagellates (Volvox)

Volvox is a hollow, spherical colony of 1000’s of individual

cells

Cytoplasmic bridges connect cells

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Volvox

Volvox displays some cellular differentiation

Non-flagellated gonidia(reproductive cells) can reproduce sexually or

asexually

Volvox is closely related to plants, but also

provides insights on animal evolution

Shows how multicellularity may

have evolved in the first animals

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Asexual Reproduction

in Volvox

Gonidium undergoes several rounds of

fission

Daughter colony forms inside parent, but is of

opposite polarity

It will invert, so future flagella will point out

Daughter colony bursts out of the

parent colony28

Phylum Choanoflagellata

600 species; marine & FW

Tiny - 10µm

Solitary or colonial; free-living or sessile

Stalked, spherical, or occur in sheets

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Phylum Choanoflagellata,

cont.

Closely related to metazoans - resemble collar cells of sponges

One large flagellum w/ base surrounded by a

collar of microvilli

Flagellum beats & collar traps bacteria &

organic molecules

Particles ingested by phagocytosis

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Phylum Retortamonada

Heterotrophic flagellates, most living anaerobically in guts of insects & vertebrates

Mitochondria often absent; survive on

glycolysis

Giardia lamblia possess4 flagella & is a

common intestinal parasite in US

Giardiasis is often contracted by drinking water from mountain

streams (“beaver fever”)

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Phylum Axostylata

Heterotrophic flagellate, closely

related to Retortamonada

Trichomonasvaginalis is the most

well-known representative

Small parasite with 4 flagella that

infects the human urogenital tract

Can be transmitted sexually

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Phylum Alveolata

Consists of 3 subphyla: Dinoflagellata, Ciliophora, & Apicomplexa

Have similar rDNAsequences

Alveoli are located deep to their cell

membranes35

Subphylum Dinoflagellata

4000 marine & FW dinoflagellate species

Possess chloroplasts via endosymbiosis & are

important primary producers

Red-brown to gold-brown in color, due to peridinin

pigment

Many contribute to planktonic

bioluminescence36

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Subphylum Dinoflagellata,

cont.

Have a complex, sculpted skeleton (theca) made of

cellulose

Theca contains sulcus& 2 flagella

Some have thick theca made of several

plates

Reproduce via binary fission & can also

encyst38

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Subphylum Dinoflagellata,

cont.Some are

endoparasites of protozoa,

crustaceans, & fish

Certain genera cause red tides (Pfiesteria)

May result in massive die-offs of

shellfish & fish

Ciguatera food poisoning in humans

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Subphylum Ciliophora

Ciliates are sophisticated protozoans; 8000+

species in FW, SW, & soil

Most are motile & solitary heterotrophs

Ciliate anatomy is analogous to animal

tissues & organs

Many have specialized somatic & oral ciliature

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Ciliate Pellicle

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Subphylum Ciliophora,

cont.

Alveoli function in Ca+2

storage

Release of Ca+2 changes ciliary beat & discharge of

extrusomes

Trichocysts: long threadlike, barbed shafts

discharged as defense

Toxicysts: longs shafts with toxin used to

capture prey

Mucocysts: release mucus spray to create sticky surface for prey

capture or to form protective cysts 44

Locomotion in the Ciliates

Ciliates are the fastestprotozoans (up to 2 mm per

sec)!

Paramecium changes directions upon colliding with

solid objects (avoidance reaction)

Depolarization (similar to action potential) is due to

Ca+2 & K+ release from alveoli

Some are sessile & highly contractile (Vorticella)

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Vorticella

Sessile ciliates with coiled stalk

Double row of cilia in ciliary membrane at top of

cell

Each cell has a long stalk with a spasmoneme (spiral

spasmin protein fiber)

Contracts rapidly to escape from predators

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Nuclei Dimorphism

of CiliatesCiliates have 2 types of

nuclei

Macronucleus: genes are actively transcribed for daily synthesis activities

Micronucleus: master copy of genome; inactive except during cell division

Shapes & numbers of nuclei vary across genera

Bean-shaped in Paramecium; string of

beads in Stentor49

Sexual Reproduction: Conjugation 50

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Subphylum Apicomplexa

(Sporozoa)

5000 species; widespread; common parasites of worms,

insects, & vertebrates

Apical complex attaches to or penetrates host cell

Anterior conoid holds digestive enzymes

Micropores (feeding pores) located on side of cell

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Plasmodium

Four species of Plasmodium that

cause malaria

#1 human parasite, infecting 300 million

people per year

1% die each year

Anopheles mosquito is the vector

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The Complex Life Cycle of

Plasmodium

Sporozoite: motile, infective stage with apical complex

Merozoite: motile, reinfectivestage with apical complex

Gametocyte: male & female reproductive stage that

releases gametes (sexual reproduction)

Spore: protective capsule secreted after gametes fuse

to form diploid zygotes

6-12 merozoites

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Plasmodium Life Cycle

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Stages of Plasmodium Life

Cycle

Sporozoites injected into blood by mosquito & attack

liver cells

Merozoites derived from sporozoites & reinfect liver

cells or move to RBCs

Cyclical merozoite release correlates with cyclical

nature of malaria symptoms

Chills, fever, fatigue (hgbloss), serious damage due to the blocking of capillaries by

infected RBCs

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Stages of Plasmodium Life

Cycle, cont.

Gametocytes form in RBCs, but do not pair

After ingestion, release gametes into the mosquito

gut

Form zygotes which penetrate gut wall & encyst to form spore

Sporozoites produced in spore & later migrate to salivary glands; released

with mosquito’s next blood meal

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AmeboidProtozoa

Have many pseudopodiafor locomotion & prey

capture (heterotrophs); complex cytoskeleton

Marine, FW, & terrestrial species

Similar to certain animal cells: archeocytes of

sponges, mammalian WBCs

3 main groups: Amebas, Foraminifera, &

Actinopoda59

Amebas

3 phyla that includes important genera such as Amoeba, Chaos, Arcella,

Difflugia

Naked or enclosed in a test (lorica, theca)

Arcella has dome-shaped test covering its top with pseudopodia extending

underneath

Chaos: 5mm long & multinucleated

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Arcella

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Chaos

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Cellular Features of

Amebas

Specialized pseudopodia

Lobopodia: wide & rounded

Filopodia: slender & may be branched

FW species have 1 or more contractile vacuoles (none in marine species)

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Phylum Foraminifera (“Forams”)

Most marine

Many branching reticulopodia (specialized

filopodia) that interconnect to form

reticulopodial network

Vesicular traffic gives reticulopodia a granular

appearance

Locomotion is via reticulopodial network:

extends, anchors to substrate, & contracts

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ForamStructure

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Single-chambered foram Multi-chambered foramwith test pores

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Phylum Foraminifera,

cont.

Forms a probing net used to find food

Test made of calcium carbonate

Most multi-chambered; start life in 1 chamber, but extend & secrete

new tests

Benthic & planktonicforams have different

tests69

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Phylum Foraminifera,

cont.

Planktonic tests are more fragile

Possess spines to increase surface area

& buoyancy

Foram tests create natural wonders in the form of chalk &

limestone

Pink sands of Bermuda, White Cliffs

of Dover, blocks of pyramids

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Phylum Actinopoda

Spherical, planktonicgroup with a perforated

test

Posses many axopodia: long, stiff, needle-like

pseudopodia

Have microtubule support rods that can attach &

retract

Used for flotation, locomotion, & hunting

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Phylum Actinopoda,

cont.Distinct cellular regions due to the presence of a layer of

pseudopodia (not actinopods)

Cortex: shroud of pseudopodia covering test

that digests prey & transfers nutrients

Medulla: inner cell body that contains the nucleus,

nutrients, or oil drops for buoyancy

Divided into two classes: Radiolaria & Heliozoa

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Class Radiolaria(Phylum Actinopoda)

Marine, mostly planktonic

Spherical test of silica (SiO2)

Large, up to 20 cm in some colonial

species

Forms radiolarian ooze

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Radiolarian Heliozoan

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Class Heliozoa(Phylum Actinopoda)

Sun animalcules

Marine, FW, or terrestrial (on

mosses)

Contractile vacuoles in FW species

Similar to radiolarians

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Heliozoan81

Phylogeny of Protozoa 82

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