514 



THE BIOLOGY OF MARINE ANIMALS 



contributes to the total coloration of the animal. Only certain colour 

 varieties are capable of background responses. In /. baltica, for example, 

 background responses are restricted to animals with light-coloured cuticle 

 (5, 37a, 54, 57, 64). 



Adaptive colour responses are a notable feature of the behaviour of 

 many decapods. The chromatophores concerned in these changes are 

 multinucleate or syncytial structures lying in the skin, and sometimes at 

 deeper levels. Each chromatophore-group contains one or several kinds of 

 pigments; white, red, yellow and often black, brown and blue. Even in the 

 polychromatic groups the pigments behave independently without inter- 

 mixture. White pigments are guanine, red and yellow pigments, carote- 

 noids, black and brown pigments, melanins. The blue pigment, which 



30 



60 90 

 (1) 



120 



750 



150 30 60 90 120 



Time (minutes) (2) 



Fig. 12.6. Chromatophore Changes in the Shrimp Palaemonetes vulgaris 

 on Black and White Backgrounds 



1 . Change in diameter of a red and white pigment mass in an animal taken from a 

 white background and placed upon a black one. 2. Change in diameter of a red and 

 white pigment mass in an animal taken from a black background and placed upon a 

 white one. (From Brown, 1935.) 



often appears outside the colour cells in a diffuse condition under certain 

 circumstances, is a carotiprotein. Species differ considerably in the number 

 and relative amounts of chromatophore pigments which they possess, and 

 this conditions the range of their background responses. 



Some marine decapods adapt themselves to a wide range of background 

 colours. Thus, Crangon can change to conform with white, black, grey, 

 yellow, red and orange backgrounds, and Palaemonetes can match back- 

 grounds of black, dark grey, white, blue, green, yellow and red (Fig. 12.6). 

 The crabs Portunus anceps and P. ordwayi also show a considerable degree 

 of colour adaptation to their backgrounds (Table 12.2), whereas the fiddler 

 crab Uca pugilator shows only weak albedo responses. It has been found, 

 however, that Uca has a well-marked diurnal rhythm, in which it darkens 

 during the day and blanches at night. Such an inherent rhythm is absent in 



