604 



THE BIOLOGY OF MARINE ANIMALS 



Rhizocephalan parasites produce profound effects on the morphology 

 and metabolism of their hosts. The Sacculina parasite of Carcinus accumu- 

 lates large quantities of lipoid reserves which in the normal female crab 

 would be deposited in the ovaries. In the non-parasitized crab the blood 

 is not tinted, except when a moult is imminent or when the ovaries are 

 nearing maturity, when it becomes coloured by carotenoids. The fat- 

 content of the blood and ovaries also increases greatly in the female at 

 sexual maturity. When infected with Sacculina, however, both sexes have 

 coloured blood and a high fat-content. Sacculina thus alters the metabolism 

 of the male crab to that characteristic of the female. In Pagurus infected 

 by Peltogaster the fat-content of parasitized animals is reduced below that 



(a) 



(e) 



Fig. 14.15. Effects of the Rhizocephalan Parasite Sacculina neglecta 

 on its Host, the Crab Inachus mauritanicus 



(a) Abdomen of normal adult female (ventral view); (b) infected female; (c) abdomen 

 of normal male (ventral view); (d) and (e) infected males. (Redrawn from Smith (94).) 



of normal animals. Rhizocephalan parasites also affect the genital organs 

 and secondary sexual characters, and so-called parasitic castration results. 

 In infected males of brachyurans and pagurids the testes become more or 

 less completely atrophied and the external sexual characters tend towards 

 an intersexual or predominantly female type. The effects are seen in the 

 shape of the abdomen, size of the chelae, reduction of copulatory stylets 

 and the appearance of abdominal appendages of female appearance 

 (Fig. 14.15). There is much variation in the extent of external modification 

 which male crabs undergo as the result of parasitization. The degree of 

 modification is correlated with size, smaller crabs being liable to greater 

 alteration of secondary sexual characteristics (21, 28, 47, 82, 83). 



The Ascothoracica are another group of parasitic cirripedes and are 

 found in corals and echinoderms. They include the Lauridae and the 



