A highly threatened crayfish, the Mistake Mountains crayfish (Euastacus jagara) belongs to the largest of the ten Australian crayfish genera. Species in the genus Euastacus, which includes some of the largest and rarest species of crayfish in the world, are often broadly referred to as the ‘spiny crayfish’ (2).
Compared with many other species in the genus, which typically possess an impressive array of spines on the thorax, abdomen and claws (2), the Mistake Mountains crayfish is poorly spinose. There are between three and six large spines, as well as additional smaller spines, on the large, pincer-like claws, but the spines on the abdomen are minimally developed. It also has a dense covering of bristles all over the body (3).
The Mistake Mountains crayfish is dark green or green-blue to orange-brown on the back, with a bluish tint to the underparts and the sides. The legs are light blue or blue-brown. The claws have a distinctive mottled pattern, with a greenish tint highlighted with a brighter blue, and the large spines are generally red, with yellow tips (3).
Like other crayfish, this large, freshwater species has a carapace that protects the head and internal organs. The six segments of the abdomen are individually encased, with a flexible membrane between them to allow movement. Crayfish also have a pair of large fore-claws, followed by four pairs of walking legs and then four pairs of small swimming legs, called ‘swimmerets’. These swimmerets are covered with fine hairs, to which the female attaches her eggs. A central tail flap is surrounded by four other flaps that are used to move the crayfish rapidly through the water, as well as curling up to form a brood chamber. The eyes are each borne on an eyestalk, while a pair of large feelers (or antennae) and a pair of small, fine, centrally-located feelers (or antennules) make the crayfish’s sense of touch and taste particularly sensitive.