colours 53 



of green algae (which have no bile pigments) the pigment slowly 

 disappears. 



The most obvious and important pigments in the Crustacea are 

 the carotenoids. These, as their names implies, are chemically 

 related to the colour in carrots; in fact one of the most abundant 

 of the carotenoids in Crustacea is /3-carotene, which is the main 

 pigment in carrots. Astaxanthin is another abundant carotenoid; 

 it is responsible for the red colour of many different crustaceans. It 

 is also responsible for the blue colour of the lobster; the blue is 

 formed when the astaxanthin is linked with a particular protein. 

 The familiar change in the colour of the lobster when boiled is due 

 to the denaturation of the protein and the breaking of its link with 

 the carotenoid pigment. A similar pigment, but more violet in 

 colour is found in the eggs of the hermit crab Eupagurus bern- 

 hardus. The eggs often contain so much of this pigment that they 

 appear to be black in colour. Lobster eggs are green in colour; this 

 is also due to astaxanthin linked to a protein, and shows the same 

 change to red when the eggs are boiled. The change to red is also 

 shown naturally by the embryos towards the end of development; 

 the green colour disappears, and the embryos become red. A similar 

 change is found in the eggs of Daphnia magna. The green colour is 

 found dispersed through the whole of the cytoplasm of the new 

 laid egg, but at the end of development the red colour is found to 

 be in small fat globules. This change in the location of the pigment 

 is due to a change in solubility w r hen the protein link is broken. 

 When linked with protein the pigment is soluble in water, but when 

 the protein link is broken the freed pigment is only soluble in fats 

 and similar substances. 



The amount of carotenoid in the body and eggs of Daphnia 

 magna has recently been found to be influenced by light. Specimens 

 kept in continuous light deposited three times as much carotenoid 

 in the fat body and eggs as specimens kept in the dark, even though 

 both groups were fed identically. The process can be reversed by 

 transferring specimens from the light to darkness, when after 

 several days they lose some of their colour. 



These experiments are relevant to the coloration of cave Crus- 

 tacea, most of which are white or transparent. This lack of colour 

 seems to be due to the lack of light in caves, and some cave species 

 have been found to gain colour when exposed to light for a number 

 of weeks. 



It might be expected that Crustacea from the deep sea might 



