Algae

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Flagellated forms

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Group

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Key Features

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Euglenoids

green, flagella (whip-like cilia),
free-swimming, red eye spot,
flexible body (<0.4 mm)

Euglena

Dinoflagellates

brown, 2 flagellae (1 in girdle),
free-swimming,
tough armour (<0.4 mm)

Peridinium
(Star of the Marshes)

Green Algae
(Chlorophyta)

spherical colonies,
cells with 2 flagellae,
(Volvox: 0.5-2 mm)

Volvox
(Jewel of the Pond)

Not all green algae are green.

tiny, green / red, often in
bird baths, (<0.05 mm)

Haematococcus
Chlamydomonas

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Non - flagellated forms

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Group

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Key Features

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Blue-green algae
(cyanobacteria)

blue-green, often slow locomotion,
used to be considered algae but more
closely related to bacteria
(cells <0.05 mm, colonies can be many mm).
The bigger cells are able to fixate nitrogen.

Anabaena

Diatoms

usually brownish, silica cell wall
in 2 parts, solitary or
colonial, some have a slow gliding
motion. (<0.5 mm)

Asterionella

Desmids
(Gamophyta)
conjugating
green algae

green, no flagella, mainly
solitary, some colonial, various shapes,
2 semi-cells which are mirror images
(<0.5 mm)

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Green algae
(Chlorophyta)

green, don't move, no flagella,
not attached to a surface.
star-shaped colony:
Pediastrum (<0.3 mm)

Pediastrum
(Star of the Pond)

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bottom right: Scenedesmus
<0.03 mm

Chlorella (symbiont
in several organisms).

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Other algae of various growth forms

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Group

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Key Features

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Water net

a sock-like colony, green algae
(related to Pediastrum)

Hydrodictyon
(The Water Net)

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Filamentous forms

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Pond scum
(Gamophyta:
conjugated
green algae)

non-branching, green chains
of cells with distinctly
shaped cell contents.
(cells <0.1 mm, chain - cms)

Spirogyra
(helical chloroplast)

Other non-
branching forms

several non-related groups

Ulothrix

Branching forms

mostly green algae

Cladophora

Red algae
(Rhodophyta)

Mainly marine, but some
freshwater forms,
not always red.

Porphyridium

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Scottish Charity Number - SC005538