COLOUR CHANGES 



TABLE J 2.2 



515 



State of Chromatophores in the Bermudan Red Crab Portunus ordwayi 

 on Backgrounds of Different Colours 



C, concentrated ; D, dispersed ; I, intermediate condition of pigments 



(from Abramowitz) 



Pct/aemonetes, but Hippolyte displays both a daily rhythm and a response 

 to environmental conditions {see p. 528). Not all decapods show such 

 colour responses, however. They are absent in Homarus, Libinia and Pagu- 

 rus, for example, and old individuals of Carcinus lose much of their early 

 ability to change their colour, and chromatophores usually become fully 

 expanded (10, 12, 21,23, 68). 



The blue pigment mentioned above is ephemeral in nature, and in 

 Hippolyte is associated with the pale nocturnal phase. Similarly, in Palae- 

 monetes, the appearance of the blue pigment is associated with blanching. 

 Thus, when a dark animal is placed on a white background, its red-yellow 

 chromatophores contract, and after a few minutes they become invested 

 by a cloud of bluish pigment which invades the surrounding tissue spaces. 

 The blue coloration lasts about an hour, and then gradually vanishes. 



Special alterations in chromatophore patterns occur during the breeding 

 season in certain decapods. In various species of Palaemon and Palaemonetes 

 the mature females develop special patches of leucophores on the egg- 

 bearing segments during the breeding season. These white pigment cells 

 are located directly over the gonads, and serve to mask the eggs and reduce 

 the shadow which they create (44). In the genus Uca there is a general 

 trend towards the development of a dazzling white carapace during the 

 display season. Field studies have shown that bright sun is necessary for 

 the maximal daily development of display-colour, and bright species reach 

 their peak in the tropical eastern Pacific where strong sunlight and high 

 tidal ranges prevail (25). 



It is now a well-established fact that the chromatophores of Crustacea 

 are under endocrine control and are not directly innervated. In the prawn 

 Palaemonetes interruption of the dorsal blood vessel abolishes colour 

 responses in the region behind the cut, and removal of the eye-stalks causes 

 the animal to darken. Injection of extracts of the eye-stalks brings about 

 contraction of the red chromatophores and dispersion of the white chro- 

 matophores in a dark animal. The active chromatophorotropic principles 

 in eye-stalk extracts were regarded as hormones, and it was thought that 



