The pea crabPinnotheres novaezelandiaeFilhol (Brachyura: Pinnotheridac) infests the musselPerna canaliculus(Gmelin) in Wellington Harbour. The crab passes through the same post‐planktonic stages as other pea crabs. The number of eggs hatching increases over summer, although females can be found incubating eggs at any time of the year. Shellfish below the level of low water neap tide are more heavily infested than those above this level. Damage to the host is restricted to erosion of the demibranchs and nodule formation on the mantle.