602 



THE BIOLOGY OF MARINE ANIMALS 



associations with other animals, and it is doubtless by this route that the 

 parasitic cirripedes have evolved. Tubicinella found attached to whales and 

 Chelonobia on marine turtles are provided with basal ramifications extend- 

 ing into the integument of their hosts; these animals, however, still feed 

 normally. But Anelasma, which penetrates into the skin of sharks, feeds on 

 the tissues of the latter by a system of ramifying roots. This is essentially 

 the mode of feeding characteristic of all rhizocephalans. 



Probably the best known of all marine parasites is the rhizocephalan 

 Sacculina. This animal lives on crabs, and in the adult condition it presents 

 the appearance of a fleshy bag lying on the lower surface of the abdomen 



Fig. 14.13. Diagrammatic Representation of the Rhizocephalan Parasite 



Sacculina carcini, Showing the Extensive System of Roots which Ramify 



through the Tissues of the Crab. (From various sources.) 



and emerging from the cephalothorax of the crab. This sac shows a small 

 orifice which leads into a flattened mantle cavity and consists largely of 

 paired ovaries together with testes and a small ganglion (the animal is 

 hermaphroditic). The sac is only the external manifestation of the parasite, 

 which also bears a system of roots ramifying throughout the body of the 

 crab (Fig. 14.13). It is by means of this root system that the parasite 

 absorbs nourishment from its host, and supplies the reproductive tissues 

 with food. 



On hatching, the larva of Sacculina has typical cirripede features and 

 resembles the nauplius of sedentary forms such as Balanus (Fig. 14.14). It 

 differs, however, in the absence of a digestive system and the interior of the 

 body is filled with lipoid food reserves. After four moults the nauplius 

 transforms into a cypris larva, which settles on its proper host and attaches 



