Art or Science?: Life in Glass Cases

Some of the most beautiful objects in the micro world can be found in the most humble of locations. look in any pond at the plants and rocks near the shoreline. Often they will be coated below the water with a brown scum like layer. If you scrape off a little of this brown scum into an airtight container you will almost certainly have collected hundreds if not thousands of these objects. What are these objects? A look under the microscope will reveal strange creatures which appear to live inside highly decorated and transparent cases, in many different shapes and sizes,

Such creatures really do exist, They are called diatoms and you can find them almost anywhere you find water. In fact they are so numerous that they produce at least 20% of the oxygen in the atmosphere. Diatoms are a type of Algae, microscopic in size and brownish in colour, and they get their energy from photosynthesis,

There are two main types of diatom: centric , possessing radial or circular symmetry and pennate having bilateral symmetry ie two symmetrical halves referring to their cases which are made of silica and transparent like glass.Some pennate diatoms move by forcing out water through a hole called a raphe. The cases are called frustules and are in two halves. They are perforated with tiny holes to enable waste to pass out and nutrients to flow in. The shapes of the cases and markings and striations are used to identify the different species of which there are many thousands.. Sizes range from 2 to 500 microns (0.5 millimetres).Diatoms can be solitary or linked in colonies in zig zag, side by side or star shaped formations.

Diatoms are fascinating to study under the microscope. They can have such intricate detail and varied shapes. I have found several species in a local stream attached to weeds and stone as a brownish scum.

A sample taken from a local stream. There are several species here of largely pennate diatoms. You can see many different shapes and at this relatively low magnification a glimpse of the ornamental detail of the silica cases. Most of the diatoms in this image are individuals.

Zooming in on a single diatom we can see the detailed striations of the silica case while inside the golden brown of the living cell. The colour is due to photosynthetic pigments which harness light energy to produce energy rich substances.