PIGMENTS AND COLOURS 491 



the underlying radial symmetry of the animal; for example, in many 

 Scyphomedusae. The close relationship between colour patterns and under- 

 lying structures is very striking throughout this phylum, and as one 

 example we may note how endodermal melanin is accumulated along the 

 mesenteric insertions in certain varieties of ' Metridium senile. Often skeleton 

 and polyps are differently coloured, as in the organ-pipe coral Tubipora 

 (Alcyonaria), in which the coral framework is bright red but the polyps 

 are brownish red with green-tipped tentacles, or entirely green in colour. 

 Beautiful and striking patterns are also seen in many polychaetes and 

 leeches, in which colour patterns are metamerically arranged, often in 

 association with particular underlying structures. Colour patterns in the 

 Crustacea, again, are frequently segmentally disposed, and in many echino- 

 derms they bear a distinct relationship to both the radial arrangement and 

 structural organization of these animals (23, 63). 



Colour patterns of the adult are sometimes preceded by distinct larval 

 patterns; for example, in pelagic stages of many teleosts and Crustacea 

 (Fig. 11.7). In decapod larvae and in mysids the chromatophores are 

 organized into definite neural, visceral and caudal groups, with accessory 

 groups on the appendages. The first three groups constitute a primary 

 system, which is retained throughout life in the mysids. In adult decapods, 

 however, they are gradually masked by the development of a secondary 

 system, homologous with the accessory group of mysids and responsible 

 for the coloration of the adult (39). Colour changes during growth have 

 been the subject of a special enquiry in the garibaldi fish Hypsypops 

 rubicunda. The young are brilliantly coloured in blue due to a layer of 

 guanine crystals overlying a melanin layer which absorbs longer wave- 

 lengths. Half-grown fish are dusky in colour and secretive, whereas the 

 adults are bright orange and use their colours as advertisements of terri- 

 torial occupation. In this species the relative quantities of carotenoid pig- 

 ments (xanthophyll esters) increase with age, and they produce the brilliant 

 integumentary colour of the adult (47). 



Inheritance of Colours 



Closely related species are often slightly dissimilar in colour and mark- 

 ings due to relative differences in the amounts of various pigments present. 

 Examples are the piper and grey gurnard Trigla lyra and T. gurnardus 

 which differ in the relative development of red and black pigments. In 

 fishes, cephalopods and certain Crustacea, integumentary pigments are 

 located in chromatophores, and the pattern and coloration in a particular 

 species depend upon the absolute abundance of different kinds of chroma- 

 tophores and their macroscopic aggregations at particular loci. Goodrich 

 (28) has presented illustrations to show the character of such chromato- 

 phore differences in teleosts, and Table 1 1.3 shows the result of a quantita- 

 tive analysis of chromatophores in certain coral reef labrids (30). 



Definite specific differences of this kind are, of course, genetically deter- 

 mined, and are transmitted from one generation to the next. In an interest- 



