panopaei" manipulates the behaviour of both sexes of the crab on which it settles, so that the host treats the barnacle's brood sac as if it contained the crab's own eggs.In the case of male crabs, the parasite causes the ventral abdominal plate to widen, which makes it more suitable for brooding, and alters the crab's behaviour so that it looks after the brood sac, despite this not being a normal behaviour for a male crab.