A swimming ostracod from a pond in Wageningen, Netherlands, with colonial ciliates on the shell.

  • Taxonomy

    Kingdom: Animals

    Phylum: Arthropods

    Subphylum: Crustacea

    Class: Ostracods

  • Location

    Fresh, brackish and marine waters, worldwide.

  • Size

    0.1 – 2 mm, a few species much larger (like Gigantocypris).


Ostracods mainly live on or in the bottom, with their solid calcified shell protecting them from damage. This shell can have different textures, ridges and/or hairs. From the shell, the legs and antennae protrude with which the ostracod swims and collects foode. Some species can produce light.

Ostracods in plankton samples are often bottom dwelling species that have been swirled up by waves or currents. There are also some free-swimming marine species, the most special being the genus Gigantocypris, which have an almost perfect spherical shell and can grow up to 3 cm in size. In fresh water ostracods that live inthe water column are more common.

Ostracods can be predators, herbivores as well as scavengers. They reproduce sexually, usually laying eggs directly in the water, or attaching to a substrate such as a water plant. From the egg, as with many other crustaceans, a nauplius larva develops into an ostracod. 

A freshwater ostracod from Wageningen, Netherlands.