Diatoms are algae, tiny single cell creatures found in pools and ponds and oceans. They are enclosed in a cell wall of silica which are mostly bilaterally symmetric. Though there is a slight asymmetry, so that one side might fit inside the other.
Remarkably they produce dimethyl sulfide which then forms tiny sulfate aerosols which are among the tiny particles that encourage water vapour to condense in our skies and fall as rain. It is a beautiful idea that through this process these tiny creatures call the water that has escaped them back to earth.
Since Victorian times, we've been arranging these tiny creatures. The middle three images are by a person called W M Grant. I am particularly partial to his or her arrangements.