Protists

Page
6

Slide 42

Eukaryotes

Common

ancestor

of all

eukaryotes

DHFR-TS

gene

fusion

Unikonta

Excavata

Chromalveolata

Rhizaria

Archaeplastida

Choanoflagellates

Animals

Fungi

Amoebozoans

Diplomonads

Euglenozoans

Alveolates

Stramenopiles

Rhizarians

Red algae

Green algae

Plants

Slide 43

Amoebozoans

Amoebozoans are amoeba that have lobe- or tube-shaped, rather than threadlike, pseudopodia.

They include gymnamoebas, entamoebas, and slime molds.

Slide 44

Slime Molds > fungus-like

Slime molds, or mycetozoans, were once thought to be fungi. Molecular systematics places slime molds in the clade Amoebozoa.

Many species of plasmodial slime molds are brightly pigmented, usually yellow or orange.

At one point in the life cycle, plasmodial slime molds form a mass called a plasmodium (not to be confused with malarial Plasmodium).

The plasmodium is undivided by membranes and contains many diploid nuclei. It extends pseudopodia through decomposing material, engulfing food by phagocytosis.

Slide 45

Life Cycle of Plasmodial Slime Mold

Feeding

plasmodium

Mature

plasmodium

(preparing to fruit)

Young

sporangium

Mature

sporangium

Stalk

4 cm

1 mm

Key

Haploid (n)

Diploid (2n)

MEIOSIS

Spores

(n)

Germinating

spore

Amoeboid cells

(n)

Flagellated

cells

(n)

Zygote (2n)

FERTILIZATION

Slide 46

Cellular slime molds form multicellular aggregates in which cells are separated by their membranes.

Cells feed individually, but can aggregate to form a fruiting body.

Dictyostelium discoideum is an experimental model for studying the evolution of multicellularity.

Slide 47

Life Cycle of Cellular Slime Mold

Spores

(n)

Emerging

amoeba

(n)

Solitary amoebas

(feeding stage)

(n)

Aggregated

amoebas

Migrating

aggregate

Fruiting

bodies

(n)

ASEXUAL

REPRODUCTION

600 µm

200 µm

Key

Haploid (n)

Diploid (2n)

Amoebas

(n)

Zygote

(2n)

SEXUAL

REPRODUCTION

MEIOSIS

FERTILIZATION

Slide 48

Protists play key roles in ecological relationships

Protists are found in diverse aquatic environments.