Ostracods belong to the class of Crustaceans, a large group of anthropods including such widely-known species like krills, lobsters or crabs. Their habitats include fresh waters and oceans alike, ostracod species being among the most varied and most wide-spread forms of Crustacean existence – they can be found in any wet place, including small ponds, even the tiny pools of water that form inside flowers.
Ostracods are fairly small, their size ranging between 0.1-32 mm. The body of an ostracod consists mainly of a large head; a thorax, the part between the head and the abdomen; a small, often inexistent abdomen and the limbs. Almost all appendages are attached to the large head: the antennae used for swimming, the mandibles, the lower, jaw-like mouthparts used for eating and cutting and the maxillae or upper mouthparts.
What distinguishes Crustaceans – and with them, Ostracods – is the two-parted limbs, that is, limbs made up of several segments and branched into two.
Ostracod species take in oxygen through the branchial plates on the surface of their body. The majority of ostracod species have no circulatory system or heart, their vital fluids circulating among shell valves. They excrete waste through glands on their maxillae or through their antennae.
Ostracod species have a very sensitive sense of touch. Their bodies and limbs are covered in sensitive hairs with the help of which they feel their way forward. Though not very well-developed, some species have a single eye or compound eyes, too.
During reproduction, the two penises of the male ostracod unite with the two orifices of the female specimen. However, numerous ostracod species reproduce in a parthenogenetic, that is, asexual way, practically cloning themselves. The eggs produced by the female are released directly into the water or laid on the surface of plants. When the eggs hatch, the larvae already have a hard shell to protect them.
1. Some Ostracod species possess a special organ that produces a bluish light as defense against predators or as a way to attract specimen of the other sex for purposes of mating.
2. Fossils have been around for more than 500 million years.
3. Ostracod eggs are incredibly resistant, being able to survive drying and remaining viable for long periods of time, even years.
Finally, what’s most interesting is that ostracods can even resist being eaten by other animals like fish or birds – when they get eaten, they close their shells so tightly that in almost 30% of the cases they are able to get out on the other end of their predator, completely unharmed.