What are Ostracoda?

Ostracods, or, scientifically Ostracoda, are a Class of small crustaceans among the most diverse aquatic arthropods, and, thanks to their easily fossilised bivalved carapaces, they have a long and rich fossil record. Over sixty thousand fossil and extant species and subspecies of ostracod have been scientifically described, and the group has utility for biostratigraphy (the art of dating sediment), palaeoecology (the description of past environments) and palaeogeography (the knowlege of past geographical frameworks). Since their appearance during the Lower Ordovician (450 million years ago), they have adapted to live in a wide range of aquatic environments, which currently includes settings as diverse as the deep ocean abyssal planes, hypersaline temporary ponds and terrestrial damp leaf litter.

Their bivalve carapace, composed of calcium carbonate, covers the entire body of the animal, protecting their soft parts and appendages. The valves can be tightly closed through the actions of adductor muscles, thus providing a closed environment that protects the animal. This carapace is likely one of the key explanations for the environmental and temporal success of ostracods. As it is often the only part of the organism to fossilise, the carapace morphology is therefore the main tool in the systematic study of fossil ostracods.

There are two main groups of ostracods, the Subclasses Podocopa and the Myodocopa, both ranging from the Ordovician to present. Podocopes occur in marine and terrestrial aquatic settings as benthos, and typically have a more heavily calcified carapace, and therefore a widespread fossil record. Myodocopes are exclusively marine, include benthic, nektobenthic and planktonic species and, as their carapace is weakly mineralised, they have an intermittent fossil occurrence.

Below, we present a gallery of photographs of different species of Ostracoda, kindly offered by members of our community of ostracod researchers. If you want to learn more about these exceptional animals we refer to the website of Dr Robin Smith of the Lake Biwa Museum, Japan.

In addition to their importance to science, ostracods have also been the subject of various works of art.