90 A BIOLOGY OF CRUSTACEA 



object first. It has been shown that mysids are sensitive to sounds 

 in water, and that they are less sensitive when their statocysts have 

 been removed. The mysidacean statocyst is peculiar because it is 

 located in the tail (fig. 40), while in the decapods the statocysts are 

 found at the bases of the antennules. 



Additional evidence that decapods can hear is derived from the 

 fact that a considerable number of species have special devices for 

 producing sound. The spiny lobsters (Palinurus and Panulirus) pro- 

 duce sounds by rasping the bases of their antennae against a toothed 

 ridge on the carapace. Two main sounds are produced by Panulirus 



CHROMATOPHORES 



TBLSON 



STATOCYST 



OUTER BRANCH 

 OP 

 UROPOD 



Fig. 40. Tail of a mysidacean (Macromysis) to show the 

 statocysts on the inner branches of the uropods. 



argus: one is a sharp rasp, which is accompanied by violent con- 

 tractions of the abdomen. This is clearly a defensive sound emitted 

 when the creature is attacked and is attempting to escape. The 

 other sound is a slow rattle which is emitted when the spiny lobsters 

 are in groups. The function of this sound is unknown, but the fact 

 that it is emitted by undisturbed lobsters when in the presence of 

 others suggests that it is for their benefit and that they have some 

 means of perceiving it. 



Some crabs of the genus Uca make rasping noises if another crab 

 looks into their burrow. Such a noise is regarded as a sign that the 



