CHAPTER VII 

 ASSOCIATIONS WITH OTHER ANIMALS 



Asa crustacean makes it way around its environment it must 

 inevitably encounter other animals; the results of these encounters 

 can vary considerably. The two creatures may ignore each other, 

 or, if the animal which is encountered is a predator the survival 

 of the crustacean will depend upon its ability to escape or deter the 

 assailant. If the crustacean is a carnivore and the meeting is with a 

 potential prey species the roles will be reversed. But apart from 

 these rather obvious possibilities there are many special relation- 

 ships which may be entered into. 



Of all the creatures with which the Crustacea come into contact, 

 the coelenterates, which include the sea anemones, corals, jellyfish 

 and their allies, seem the most prone to enter into special relation- 

 ships. The crustacean may merely be a predator on a particular 

 coelenterate, like the fresh-water cladoceran Anchistropus on 

 Hydra, but there are other more complex relationships. 



Hyperia galba is an amphipod which lives in the pits on the 

 undersides of large jellyfish. It was once thought that no harm was 

 done to the jellyfish, but recently it has been found that the amphi- 

 pod actually eats some parts of its host. Several species of an allied 

 genus, Phronima, live in the large spaces inside salps, which 

 although they are not coelenterates resemble them in texture. 

 Phronima has enormous eyes and peculiar modifications of some 

 of the limbs (fig. 43); the body is very transparent, making it incon- 

 spicuous within the equally glassy body of the host. Most of trie 

 salps with Phronima inside are dead and so that it seems as if the 

 amphipod is a predator which gets inside the salp and eats it. 



The coral gall crabs (Family Hapalocarcinidae) live within the 

 colonies of various corals, and produce galls by stimulating the 

 colony to develop a chamber in which the female crab lives and 

 communicates with the outside via a series of small holes. The crabs 

 obtain their food by filtering small particles from the water which 

 they cause to circulate in and out of the chamber. The male crabs 

 are much smaller than the females and can enter the chamber 



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