The sporozoanThelohania contejeaniHenneguy (Microsporida: Nosematidae) is recorded fromParanephrops zealandicus(White) for the first time. It is an intracellular parasite invading musculature throughout the crayfish, causing a gradual decrease in locomotor activity, and it may eventually cause the death of the host. Infected crayfish were found in the northern part of Leith Stream, Dunedin, where the infection rate reached a maximum of 20%. This parasite has formerly been recorded only from Northern Europe.