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Ostracods are minute crustaceans living in habitats ranging from deep-sea to high mountain lakes. They are true living fossils that have existed on earth for at least 500 million years. They regulate their tissue oxygenation levels behaviourally by migrating to sediments where the oxygen levels are slightly higher than those required by their tissues (see article by Corbari, Carbonel and Massabuau, pp. 4415-4425). Cylindroleberis mariae photographed by L. Corbari and J.-C. Massabuau.