We describe the gill anatomy of Margaritifera auricularia, including a histological analysis of the marsupium, its brooding capacity and the length of the maturation process, providing information on the hitherto unknown reproductive strategy of French populations. Ova and developing embryos from the Charente and Creuse river populations were found in March, with glochidial release occurring in April. Development from first cleavage to glochidial maturity took 25-37 days. Compared with the Spanish populations, the reproductive period begins some weeks later. The estimated number of larvae per gravid mussel was around 2,000,000. We expect the findings presented here will improve captive breeding projects that aim to conserve the few remaining populations of this endangered species in Europe.

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