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.