CHAPTER IV 

 COLOURS 



The variation in colour and pattern among Crustacea is so great 

 that a mere catalogue would be larger than this book. Some of 

 the colours can be related to a particular crustacean's way of life, 

 but other colours appear to be functionless, though this may only 

 be due to our ignorance. 



Many crustaceans have concealing coloration, and merge success- 

 fully with their backgrounds. The common Porcelain Crab, 

 Porcellana platycheles, of European shores, is often extremely 

 difficult to spot when a stone is turned over because its colour and 

 texture match the mixed growth of plants and animals coating the 

 underside of the stone. Sometimes the colours are specially adapted 

 to a particularly limited environment. The small crab Haenia 

 proteus has a body shaped like a part of the calcareous green seaweed 

 Halimeda, and its colour matches that of the alga so closely that 

 detection is extremely difficult. 



Crustaceans belonging to different groups sometimes show 

 parallel adaptive coloration. An alpheid shrimp, a squat lobster, a 

 porcelain crab and a spider crab are all found among colonies of 

 Spongodes, which is a relative of the sea anemones, found in 

 Indian Seas. The four different Crustacea are all coloured greyish- 

 white with pink spots so that they resemble parts of the colony on 

 which they live. Shrimps with alternate bands of yellow and purple 

 sound most conspicuous, but several species are known which live 

 on a sea lily (not a plant, but an animal belonging to the Echino- 

 dermata) coloured in the same way. 



Sometimes an animal is more conspicuous because of the shadow 

 that it casts. The ghost crab Ocypode ceratophthalma is coloured 

 like the tropical sands over which it runs at great speed. When 

 running it holds its body high on long legs, and the shadow that it 

 casts is more conspicuous than its body. When alarmed this crab 

 races away wildly, then suddenly stops and lowers its body close 

 against the sand so that its shadow disappears. The body is very 



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