Asterionella is a genus of pennate

Pennate

Pennate is used to mean "winged", "feathered" or simply "shaped like a wing". The latter definition is sometimes used to describe plant leaf morphology .Pennate diatoms are bilaterally symmetrical, and belong to the order Pennales....

 freshwater

Freshwater

Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...

 diatom

Diatom

Diatoms are a major group of algae, and are one of the most common types of phytoplankton. Most diatoms are unicellular, although they can exist as colonies in the shape of filaments or ribbons , fans , zigzags , or stellate colonies . Diatoms are producers within the food chain...

s. They are frequently found in star shaped colonies of individuals.

Description

Asterionella average cell size is 60-80 micrometer long and 2-4 micrometer wide.
It forms colonies that often consist of eight cells, but can vary up to 20 cells. The cells in the colony are attached by the apex by extracellular matter. By the way the cells are attached to each other, the colonies often look like stars or spiralling chains.

Reproduction

The diatom cell consists of an epitheca and an hypotheca. During asexual reproduction both thecae form the epitheca of the new daughter cell and each daughter produces a new hypotheca. Therefore one daughtercell is always smaller than the original cell.
In order to regain their original size, it is usually assumed diatoms have to reproduce sexually, although this has not yet been observed in A. formosa. However, there may also be other ways to rejuvenate.

Ecology

Asterionella formosais known to be susceptible to the chitrid fungus Zygorhizidium planktonicum. Asterionella have no means of locomotion. It is most likely a combination of gravity and currents that distribute the organism.

Some species

A. bleakeleyi

A. formosa

A. gracillima

A. glacialis

A. japonica

A. kariana

External links

Algaebase