The Murray crayfish, Euastacus armatus, is a large, spiny, freshwater crayfish (Fig. 1 A), from south eastern Australia. Like the northern hemisphere astacid crayfish, Euastacus and other parastacids assume a defensive posture when they are provoked: the chelae are raised, the legs are spread out, and the abdomen is extended. In Euastacus, the abdominal extension is accompanied by a clearly audible hiss. This sound is produced by abdominal stridulatory organs in which bristles projecting from the posterior edges of the abdominal tergites rub over ridges on the surfaces of the tergites of the next posterior segment (Fig. 1 B, C). Extension of the abdomen causes the 6 mm wide field of tergal ridges to rotate forwards and under each row of bristles. Sound production either in air or in Water can be silenced by coating the hairs with vaseline or by shaving them off...

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