CRUSTACEANS 



Whale- Louse (Cyamus ceti) is exceptional among the members of 

 the sub-order in having its body flattened from above downwards, 

 and it is found parasitic on the skin of whales, to which it is 

 enabled to hold fast by 

 means of strongly -hooked 

 legs. The abdomen is re- 

 duced to a mere stump en- 

 tirely devoid of appendages. 

 The weird-looking Skeleton 

 Shrimps (Caprella] are also 

 distinguished by the presence 

 of a much-reduced abdomen. 

 They are found climbing like 

 monkeys among the branch- 

 ing colonies of various zoo- 

 phytes. 



2. Isopods (fig. 256) differ 

 from Amphipods in being 

 flattened from above down- 



ABDOMEN 



Fig. 255. Amphipods (enlarged) 

 A, Sand-Hopper ( Talitnis locusta] ; 2-8, last seven segments of 



wards while the abdomen is tnorax > tne first is fused with the head - B > whaie-Louse (Cyamus 



ceti}. c, Skeleton Shrimp (Caprella}. 



shortened and bears plate- 

 like appendages. Most of the species are marine, and of these 

 Cirolana, Idotea, and Sphceroma may be taken as typical British 

 genera. Some, however, are 

 fresh - water, as, e.g., the 

 common native Fresh-water 

 Shrimp (Asellus aquaticus), 

 distinguished by its long 

 limbs; and still others are 

 terrestrial, of which the most 

 familiar is the Wood- Louse 

 {Oniscus murarius\ com- 

 monly found Under damp F te- 256. Isopods (enlarged) 



crrm^c anrl in cimilar r1ar^c n-viii, Free segments of thorax, the first is fused with the 



piaCeS. nead A> Cirolana borea i is . B> Wood-Louse (Oniscus murarius). 



Some of the Isopods are 



curiously modified to fit them for a parasitic life, and these will 



be mentioned elsewhere. 



