Description and use of

Hydrological exchanges between rivers and groundwater are essential for many ecosystem processes: identifying their location requires a set of physical, chemical and biological indicators. Here, we describe Schellencandona rhodanensis sp. n. (Ostracoda, Candoninae), a species highly sensitive to hydrologic exchanges in river sediment. The new species is close to Schellencandona triquetra (Klie, 1936), but mainly differs in the shapes of the female genital lobe and the male hemipenis. The species is described from the Rhône River watershed, where it occurs in at least five tributaries. It is a stygobite species (i.e. a groundwater specialist), occurring in both the main channel and associated wetlands, with a maximum abundance at depth of about 1 m below the sediment surface. While S. triquetra is collected in a wide range of groundwater habitats, S. rhodanensis sp. n. is mostly restricted to river interstitial habitats fed by groundwater. It can be used as a biological indicator of interstitial habitat stability and to locate groundwater upwellings in river bed sediment.