<Emphasis Type="Italic">Cytherella</Emphasis> as a tool to reconstruct deep-sea paleo-oxygen levels: the respiratory physiology of the platycopid ostracod <Emphasis Type="Italic">Cytherella</Emphasis> cf. <Emphasis Type="Italic">abyssorum</Emphasis>

The reconstruction of past climates is a major challenge. One approach is the use of paleoceanography, which looks for clues to the past activity of deep-sea currents by associating them with the melting of the poles. In different sampling zones, fossil biomarkers are used to reconstruct the oxygenation levels of the sea bottom. Among the ostracods (crustaceans), the family Cytherellidae is considered to be resistant to significant decreases in oxygen and their fossil valves are used as biomarkers for oxygenation levels in the past. We studied the basic principles behind Cytherella cf. abyssorum’s ability to adapt to variations in water oxygenation levels in an attempt to determine what could differentiate it from other ostracods. Cytherella cf. abyssorum Sars 1866 has an activity level and ventilatory frequency only half that of ostracods studied previously. When subjected to a decrease in oxygenation, it demonstrates the beginnings of ventilatory adaptation which is unknown in the other studied ostracods. Some morpho-functional aspects are also remarkable, such as the presence of thick valves, which can close hermetically by means of powerful adductor muscles. Compared with already studied ostracods, Cytherella cf. abyssorum has, therefore, characteristics which suggest an ability to present increased resistance in hypoxia. We discuss these results in the paleoceanographical context by describing a scenario suggesting why an increased proportion of the ostracod population could indicate the existence of ocean bottoms with low oxygenation.