Planktonic Unicellular and Colonial algae

By Algal Web

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Phylum Chlorophyta


Colonial Chlorophyte: planktonic, sometimes bloom-forming. Colony is very dense, making cells hard to see; contains yellow oil droplets which can be squeezed out under a coverslip


This alga is characteristic of shallow water which dries out regularly, such as bird-baths, which it stains a blood-red colour.

Haematococcus is a chlorophyte, though it doesn’t look it at all, thanks to the haematochrome pigment. The spherical cells are actually cysts, which enable Haematococcus to survive desiccation.

This is a vegetative cell: the cell wall is visible, and two flagella (arrowed) can be seen emerging; the vegetative cells are motile.

Vegetative cells of Haematococcus

This cell shows the protoplasmic extensions between the protoplast and the cell wall (just barely visible), which are characteristic of Haematococcus


Eudorina is a colonial flagellate, related to Volvox. The colonies spin rapidly through the water. This one was found in a temporary ‘pond’ – a tyre-track in a barley field. The two flagella are just visible in some of the cells.


Pandorina is similar to Eudorina but the cells are packed closely together and often angular as a result.

Paulschulzia tenera

Colonial Chlorophyte:cells or cell groups in clearly defined spherical mucilage envelope, with individual sheaths and flagellum extending beyond outer envelope


Cells united to form a circular flat plate. Outer cells frequently bear a pair of horns, and there may be gaps between cells


Chlorella from a culture.


Formerly known as Selenastrum capricornutum, this unicellular green alga is Pseudokirchneriella subcapitata, widely used as a test organism in toxicity testing.


Spindle-shaped cells, either solitary or lying parallel in groups of 4 or 8. Some are ornamented with apical or medial spines: these have recently been placed in the genus Desmodesmus. This one is Scenedesmus dimorphus.

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