Today’s alga is asterionella.
Source: NOAA Photo Library on Flickr.
Asterionella is a genus of freshwater diatoms, usually forming star-shaped colonies of individuals.
A diatom is a unicellular alga of the Chromalveolata Kingdom which, to be honest, means nothing at all to me because this is clearly using a taxonomic system updated since my high school biology class. Anyway, diatoms are unique in that they have a hard cell wall made of silica called a frustule; although frustules take many shapes, they are usually almost bilaterally symmetrical, but never perfectly symmetrical. The fossil record suggests they appeared around the early Jurassic. Only male diatoms have flagella to get around with.
Asterionella organisms are unicellular, of course; each cell/organism is about 60-80 micrometres long (a human hair is 90 micrometres wide) and 2-4 micrometres wide. They are tiny. Usually eight such cells will gather into a colony, but sometimes as many as 20 individuals will attach. These colonies are usually star- or spiral-shaped. They have no way of moving themselves, and so rely on the whims of gravity and water current.
Posted by Christian H.