These tiny crustaceans in the class Ostracoda have a paired shell, rather like a bivalve mollusc. They are extremely common in nearly all freshwater habitats and are often some of the first animals to colonise a new pond or even puddle. Most species are small, around 1mm, so easy to overlook. They have a head and a thorax, with the head bearing two pairs of antennae that emerge from between the shells for swimming. Most are detritivores but some species feed on algae, bacteria or plants. They are very difficult to identify to species level, requiring high power microscopy.

All freshwater habitats.

All year.

Very common.

Common.