Diversity of Protists

Protists

Diverse group of mostly unicellular eukaryotes, excluding animals, plants and fungi. Reproduce using sexual/asexual strategies. “Protozoa” used to designate a group within protists.

Mixotrophs

Protists that can use both photoautotrophic and chemoheterotrophic modes of nutrition. Example; Euglena

Clusters of Protists

Excavata

SAR
Archaeplastida

Amorphea

Excavata Cluster

Unicellular protists with a modified mitochondria and distinct flagella, lack a cytoskeleton.
Modes of Living - Heterotrophs, photoautotrophs, symbiont and parasites

Three subgroups; Diplomonads, Parabasalids, Euglenozoans

Diplomonads

Unicellular, heterotrophic flagellates, lack plastids and live in anaerobic environments. Contain various parasites

Parabasalids

Unicellular, heterotrophic flagellates, have modified mitochondria (Hydrogenosomes), live in anaerobic environments.

Euglenozoans

Have one or more flagella with a crystalline rod, consists of diverse modes of nutrition (photoautotrophic, heterotrophic, mixotrophic)

Two subgroups; Kinetoplastids and Euglenids

Kinetoplastids

Parasitic euglenozoans with a structure called ‘kinetoplast’, dense network of circular DNA within mitochondria.

Euglenids

Euglenozoans with a structure called ‘pellicle’, mesh of protein strips internal to the plasma membrane

SAR Cluster

Originated via secondary endosymbiosis (non-photosynthetic eukaryote engulfed a photosynthetic red alga, introducing plastids)

• Three distinct lineages: Stramenopiles, Alveolates and Rhizarians

Stramenopiles

Unicellular and multicellular group of protists with exactly two flagella, one covered by hair-like projection (ex; giant kelp)
Three subgroups; Diatoms, Brown Algae, Oomycetes

Diatoms

Diverse unicellular algae, contain a two-part silica based cell wall.
Ecological Significance;

• Produce 20% of breathable oxygen, act as primary producers in marine/freshwater ecosystems

Brown Algae

Large, multicellular algae (ex; kelp/rockweeds).
Contain brown pigment allowing it to absorb light at low depths
Cell wall composed of cellulose and alginic acid

Plant-like appearance, but lack true roots/stems/leaves
Ecological Significance:

• stabilize sediments, primary producer, source of glumate

Oomycetes

Filamentous, heterotrophic, resemble fungi

Cell wall made of cellulose, cell covered by filamentous structure

Ecological Significance:

• Decompose organic materials

• Pathogen of animals/plants

Alveolates

Protists with membrane-bound sacs called ‘alveoli’.
Alveoli create a continuous/flat layer beneath the plasma membrane

• Skin-like support

Three subgroups; Dinoflagellates, Apicomplexans, Ciliates

Dinoflagellates

Unicellular, aquatic protists with various modes of nutrition.
Presence of overlapped cellulose plates supporting alveoli
Two Flagella:

• One wraps around a groove in the middle of the cell, other extends outward

Ecological Significance:

• primary producer, contribute to bioluminescent in the ocean

Apicomplexans

Unicellular, parasitic protists with complex lifecycles (sexual/asexual stages and multiple hosts)

Flagella and cilia not present

Unique organelle complex called ‘apical complex’ for invading hosts

Ecological Significance:

• Plasmodium; responsible for malaria transmission between mosquitoes and humans

Ciliates

Unicellular, heterotrophic protists, many feed on bacteria and other protists.
Presence of cilia, function for feeding/movement

Presence of two nuclei;

• Large nucleus responsible for most cellular function

• Small nucleus responsible for asexual binary fission

Ecological Significance:

• used as bioindicator for water quality tests

Rhizarians

Protists based on genetic similarities, morphologically diverse.

Presence of pseudopodia, thread-like extensions of plasma membrane:

• Used for movement/feeding, absent in other ‘amoebas’

Mineral shells composed of calcium carbonate produced

Archaeplastida Cluster

Primary endosymbiosis mechanism responsible for its origin, heterotrophic protists engulfed a cyanobacterium.

Cell wall composed of cellulose

Three distinct lineages; red algae, green algae and land plants

Red Algae

Multicellular protists with red pigmentation

Flagella is absent

Ecological Significance; primary producer in marine ecosystems, contribute to reef-building by depositing calcium carbonate (Coralline Algae)

Amorphea Cluster

Maximum of one flagella, two distinct lineages: Amoebozoans and Opisthokonts

Amoebozoans

Protists including slime molds, tubulinids and entamoebas

Unicellular or multicellular

Locomotion and feeding using lobe-shaped pseudopodia

Ecological Significance;

• Important Decomposers

Slime Moulds

Protists known for their ability to form large, multicellular structures

Plasmodial slime molds form brightly coloured mass within a single, multinucleate cell

Cellular slime mold aggregate into multicellular mass
Ecological Significance

• Important Decomposer

• Bio-inspired algorithms

• Network optimization in civil engineering