The large creatures in this image that look like mummy cases are diatoms. Diatoms are protists that grow a silica shell around themselves. When diatoms divide, each offspring takes half of the original shell with it, and grows another matching half to complement the inherited shell portion.
These diatoms are shown here growing on duckweed plants found in a pond. The smaller creatures around the diatoms are various species of bacteria. Diatoms are frequently found in wet environments.
Diatoms also grow on most soil. They grow on the surface layer of soil, where they can use sunlight to produce food via photosynthesis.
There are two basic types of diatoms: round ones and elongated ones, like these. Elongated diatoms can move themselves about; round diatoms cannot.
There may be as many as 10,000 species of diatoms. Huge accumulations of fossilized diatoms make up diatomaceous earth, which is used in toothpaste and in filters.