PIGMENTS AND COLOURS 487 



which have been made to explain the mobilization and transfer of caro- 

 tenoids during reproduction are that they act as fertilization hormones, 

 and that they form a vitelline reserve to supply the developing chromato- 

 phores of the embryo with pigment. In eggs of the sea-urchin Paracentrotus 

 lividus the total quantity of carotiprotein decreases during early develop- 

 mental stages, i.e. it appears to be metabolized. Regeneration of pharynx 

 and tentacles in Actinia equina proceeds normally even when carotenoids 

 are deficient. Carotenoids are sometimes associated with the development 

 of sexual coloration, especially in fishes where, as in the lumpsucker 

 Cyclopterus htmpus, considerable amounts of astaxanthin appear in the 

 skin during the summer spawning period (31, 35, 60). • 



Certain other functions of carotenoids in animals are more firmly 

 established. Vitamin A can be formed from a number of carotenoids in 

 animals, and is involved in the visual process. Rhodopsin, the photolabile 

 visual pigment, consists of a protein linked with vitamin A x as a prosthetic 

 group, and is found in marine fishes and higher vertebrates. In euphausiids 

 (Meganyctiphanes norvegica) the majority of the vitamin A (over 90%) and 

 a high proportion of the astaxanthin are contained in the eyes (12). 



Melanins and purines are utilized extensively for external coloration, 

 and the former are frequently present in the photoreceptors of many 

 invertebrates. The functional role of naphthoquinones in echinoids is still 

 obscure. In various proportions they colour the exterior of these animals 

 (Table 11.2), but the precise part they play in the internal economy of 

 sea urchins still awaits elucidation. Echinochrome is released from the 

 ripe eggs of Arbacia, and is considered to have a stimulatory effect upon 

 spermatozoa. 



Environmental Influence on Colour 



Special diets often influence the colour of animals, and some examples 

 have already been cited for polyclads and gnathiids. Another interesting 

 case is the dog-whelk Nucella /api/Ius, which frequently has brown and 

 purple pigmented shells and purple coloured eggs. These colours depend 

 upon the food of the animal, and occur in those specimens which have 

 been feeding upon mussels. Whelks, feeding exclusively upon Balanus, lack 

 purple and brown pigments (61). An analogous case is the Japanese top- 

 shell Turbo cornutus which, under experimental conditions, has a white 

 shell when fed brown alga (Eisenia), and develops shell colour when cal- 

 careous algae are added to its diet (40). 



Of physical environmental influences affecting colour, light often has 

 pronounced effects. Besides the rapid colour-responses of Crustacea, 

 cephalopods and vertebrates, slower and more durable colour alterations 

 take place. In certain coelenterates there is some correlation between light 

 intensity and degree of pigmentation. The anemones Actinia equina, 

 Anemonia sulcata and Tealia felina augment their pigments, including 

 carotenoids, under increased illumination. In Anemonia sulcata this may 

 simply be the result of an increase in symbiotic algae, and consequently of 



