CAROTENOIDS 



by Fox and Moe ; ^ ^ traces of carotene were also present. The green 

 variant was not examined. 



A pigment closely related to astaxanthin occurs in Gorgonia and 

 Pennalia spp. ^ 2' ^ ^ 



Lederer^ considers the early work of Krukenberg on corals to be 

 inaccurate, but gives no evidence to support this view. Karrer and 

 Solmssen* found no carotenoids in Asteroides calyculans. 



Formation 



(i) Nutritional Factors 



Schultze's 1 ^ early work had suggested that pigmentation of Hydra 

 depended on the nutrition of the animal, so it was not unexpected 

 that experiments on Actinia equina indicated the alimentary origin of 

 its carotenoids. ^ ^ Animals raised from eggs on a carotenoid-free diet 

 were without carotenoid pigmentation and starved animals placed on 

 the same diet regenerated the pharynx and tentacular cycles containing 

 only traces of carotenoids ; these animals were pigmented as soon as 

 carotenoids were made available in the foodstuffs. Evidence that these 

 animals can alter ingested carotenoids is less clear, but it is extremely 

 interesting to note that starved " reds ", or *' greens ", or " browns " 

 always regained their original colour when fed the same carotenoid-rich 

 diet (shrimps' eggs). 



No full explanation of the formation of different carotenoids is yet 

 available ; Fox and Pantin " suggest that it may be due either to 

 selective assimilation of carotenoids or to selective metabolism. 



In the case of Metridium senile the pigmentation is not so labile, 

 for Fox and Pantin ^'^ found no colour changes when these animals 

 were exposed for long periods to varying conditions of nutrition. It 

 has already been noted that differently coloured types contain different 

 amounts of carotenoids, so these two facts together suggest a genetical 

 disposition to store a certain amount of carotenoids which is to a great 

 extent independent of the environment. This further implies that M. 

 senile either has the ability to synthesize carotenoids de novo ; or, 

 more probably, does not utilize stored carotenoids under any conditions. 



(ii) Effect of Light 



Studer ^ ' and Elmhurst and Sharpe ^ ® have investigated the effect of 

 light on pigmentation (? carotenoid), the former in Hydra species and 

 the latter in A. equina, Anemonia sulcata, and Tealia felina. In all 

 species high light intensity stimulated increased pigmentation. As 

 might be expected from the results of the nutritional studies, M. senile 

 is not susceptible to changes of light intensity. " ' 



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