CHAPTER 1 1 

 PIGMENTS AND COLOURS 



Innumerable of stains and splendid dyes, 



As are the tiger-moth's deep-damask'd wings. 



John Keats 



Marine animals show a great range of colours, shades and patterns, some 

 of them very striking and beautiful. The most brilliant hues are to be found 

 in animals living in shallow waters of tropical seas among the groves of 

 corals, gorgonians and alcyonians where multicoloured reef fishes swim 

 or sleep. Even in cold northern seas many animals have intricate patterns 

 of great beauty : an appreciation of these may be gained from the coloured 

 plates in Mcintosh's Marine Annelids, Stephenson's Sea Anemones and 

 Mehuet's Etude de la Mer, to mention three beautifully illustrated vol- 

 umes. Animal colours are due largely to reflected light of solar origin but 

 there are, of course, some self-luminescent animals that emit light of 

 various colours; a description of these animals is reserved for another 

 chapter. 



ANIMAL PIGMENTS AND STRUCTURAL COLOURS 



Two agencies are involved in producing the coloration of marine animals, 

 namely, pigments that by special absorption characteristics give rise to 

 coloured light, and structural modifications having optical effects that 

 produce colours. Either one or other method of colour production may 

 predominate in any species, or both may occur simultaneously and play 

 complementary roles. Owing to the predominant influence of colour in 

 human visual sensations we tend to emphasize and unduly magnify 

 colour, and it is likely that many of the colours to be seen in marine 

 animals may themselves have no biological significance. Many animals 

 contain brightly coloured tissues and organs lying within their bodies, 

 and concealed from view, e.g. the body wall and gonads of many gastro- 

 pods and bivalve molluscs. There are other animals, brightly coloured, 

 which are tubicolous and normally never emerge from their burrows — 

 for example, the polychaetes Amphitrite johnstoni and Myxicola infundi- 

 bulum, both bright red in colour. Many planktonic animals are translucent 

 and colourless, or nearly so; Crustacea and fishes from mesopelagic and 

 bathypelagic waters are as a rule uniformly black, red or dark brown; and 

 it is in the littoral and neritic zones that the greatest variety of coloured 

 animals is to be found. 



Pigments responsible for animal colours often have a superficial loca- 

 tion, e.g. pigments located in the epidermis and dermis, or deposited in 



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