472 



THE BIOLOGY OF MARINE ANIMALS 



receptors, in gonads, glands, muscle and integument. They are regular 

 components of chromatophores in some animals, including crustaceans and 

 fish; they occur in the eggs of many species; and they are accumulated to a 

 notable degree in the gonads of a great many marine animals. 



Carotenoids of various kinds are present in protozoans (both holophytic 

 and holozoic forms). The transitory blooms and red tides sometimes seen 

 at sea are caused by dense accumulations of coloured species containing 

 carotenoids (Noctiluca, Gonyaulax, etc.). Carotenoids are also responsible 

 for the bright yellow, orange, red and purple colours of many sponges 

 (Halichondria, Suberites, Tethya, and many others). Echinenone and 

 y-carotene have been found in the red sponge Hymeniacidon perleve, and 

 astacene has been extracted from Axinella crista-galli (16, 71). 



Carotenoids are common in coelenterates and they are often responsible 

 for the bright red and yellow colours of these animals. They occur in the 

 Hydrozoa (Clava, Nemertesia), Scyphozoa (Lucernaria), Alcyonaria 

 (Gorgonia), Actiniaria (Epiactis), Madreporaria (Caryophyllia), and are 

 probably present in all branches of this great phylum. Sea-anemones, 

 which have been most intensively studied, contain both carotenes and 

 xanthophylls. The beadlet anemone Actinia equina exists in several well- 

 known colour varieties, red, brown and green. Brown and green varieties 

 yield an orange carotenoid, and the red variety a red acidic carotenoid, 

 actinioerythrin. The latter is conjugated with protein in the living animal. 

 In the green variety there is also a reddish-orange xanthophyll which 

 forms a green pigment in combination with protein (23, 65). The plumose 

 anemone Metridium senile is another species exhibiting manifold colour 

 forms (Fig. 1 1. 1). A variety of carotenoids occurs in this species : in general, 

 the red forms contain the greatest quantities of these pigments, whereas the 

 melanistic brown varieties yield smaller quantities but a greater range of 

 different carotenoids (Table 11.1). Metridium senile stores carotenoids 



TABLE 11.1 

 Colour Varieties of Metridium senile 



Note: principal carotenoids are shown in italics. Metridene is an epiphasic ester distinct from astacene. 



(From Fox and Pantin (23).) 



