This is called moulting. There are two species of koura found only in New Zealand. It lives in fresh water such as streams, lakes and ponds, and even in swamps. Koura shelter between stones on gravelly bottoms but they can burrow into muddy bottoms, and will burrow well down into swamps that dry out over summer, to wait until the water returns. Survival Koura need oxygen like all living animals and plants which they get from the water through their gills, under the thorax where the legs join the body.
Water is sucked in, pumped forwards over the gills and out through the mouth.
If the gins get clogged they can back-pump to flush out any debris. Koura use their four pairs of walking legs to get around quite quickly - they do not crawl as their common name, 'crawly', suggests. They also have a sort of reverse gear, to shoot back into shelter when alarmed, by flicking their tail forwards violently. Their first pair of legs, their pincers, are used mainly for catching food, for fighting with invaders, or for waving menacingly at intruders. They can give a painful nip, so be careful.