146 



THE BOOK OF NATURE STUDY 



FlG. 69. The edible crab (Cancer edulis). 



which are sheltered beneath the shell or carapace. It is because 

 the gills are sheltered in this way that the crab can tolerate the 

 absence of water in a way that would be impossible for a prawn, 

 for example, where the gills are not so thoroughly protected, and 

 where they would consequently soon dry up if the animals left the 



water, while those of the crab, 

 which are enclosed in a special 

 chamber, retain their moisture 

 for a long time. Note also the 

 movable stalked eyes, and the 

 way in which they are placed in 

 sockets into which they can be 

 withdrawn if danger threatens. 

 The same thing is true of the 

 antennae. In short, a crab is 

 a typical shore animal, well 

 adapted for life between tide- 

 marks, but not well suited for the open water where its cousin 

 the Norway lobster is quite at home. 



Very young specimens of the edible crab (Cancer edulis) are also 

 not uncommon on the shore, and may be kept in confinement with- 

 out difficulty. They 

 do not, however, show 

 the interesting colour 

 change of the shore 

 crab. 



Related are the 

 various spider-crabs, 

 of which we have a 

 considerable number. 

 All are recognisable 

 by the elongation of 

 the legs which gives 

 them their popular 

 name, and which is 

 a great assistance to 

 them in crawling about the rocks and stones of the pools. The 

 smaller forms live well in captivity. They do not show the 



FlG. 70. The common spider-crab (Hyas araneus}. A 

 cleaned specimen with most of the hairs removed. 



