Sur l'attaque de la coquille des bigorneaux Littorina Littorea (L.) de Hollande par Polydora

In Brittany, when the shell of the farmed oyster becomes covered with too many green algae, retaining the mud, farmers usually scatter some winkles Littorina littorea (L.) into their ponds; these alga-eating animals free the oysters from this adventitious vegetation, they eat the "moss" as the farmers say (1). This year, the oyster farmers from the Morbihan could not find enough (and at a decent price) winkles on the French market and had to import them from the Netherlands. These Dutch winkles did well with the removal of the algae, but showed a specificity which troubled the farmers: all the oyster shells were mutilated; their apex was gone, as if it had been eaten away by some invisible enemy. I was charged by the Marine Fisheries Scientific and Technical Office to study this phenomenon. I will briefly summarize it.