56 A BIOLOGY OF CRUSTACEA 



There are other pigments in Crustacea, but we know very little 

 about them; one such pigment is the green colour found in some 

 ostracods and in the Notostraca. This turns brown when alkalis are 

 added to it, but returns to green in acid, and it is decolorised by 

 reducing agents, regaining its colour in aerated water. 



When a crustacean colour is functional, for instance in conceal- 

 ment, the pigment is usually near the outer covering, most often 

 in special structures called chromatophores. These are sometimes 

 very elaborate, formed from several cells and having numerous 

 branches which radiate from a central body. The most complex 

 types contain four different pigments. Crangon has some chromato- 



Fig. 28. Diagram of a dichromatic chromatophore in the 

 fully expanded state. The structure is shown as being in 

 two dimensions, but the branches frequently extend in 

 all directions. The branches of the paler pigment follow 

 those of the darker pigment very closely. 



phores with black, white, yellow and red branches, while Penaeus 

 has some with white, yellow, red and blue branches. It is only in 

 the Decapoda Natantia that such multicoloured chromatophores 

 are found, most other groups can only muster one or two colours 

 in a single chromatophore. When a single colour is found in a 



