ASSOCIATIONS WITH OTHER ANIMALS 



99 



Fig. 43. Phronima sp. (Amphipoda) from inside a salp. 

 Actual length 13 mm. 



through the small holes, for the purpose of mating and fertilising 

 the eggs. A shrimp, Paratypton siebenrocki, has similar habits. 



Sea anemones are rarely eaten by other animals, they appear to 

 be distasteful, and they are well provided with stinging cells which 

 are virulent enough to repel most would-be predators. Several 

 crustaceans have taken advantage of these distasteful properties 

 and gain protection by associating with the sea anemones. A 

 recently described example is the mysidacean Heteromysis actiniae, 

 which lives among the tentacles of the sea anemone Bartholomea 

 annulata in the Bahamas. A more active use of a coelenterate for 

 protection is made by the small crab Lybia tessellata, which carries 

 a small sea anemone in each chela and thrusts them at its predators. 

 It has been suggested that Lybia may also use the stinging 

 powers of the anemones to disable small animals, which the crab 

 then takes as its own food. 



The associations between hermit crabs and sea anemones are 

 classical examples of commensalism. This is a term applied to 

 associations in which the two partners share the same food. Most 

 hermit crabs hide their soft vulnerable abdomens in an empty 

 mollusc shell. Eupagurus bernhardus is found most frequentlv in 

 empty whelk (Buccinum) shells; this too is a special relationship. 

 Even though the whelk is not a living partner the hermit depends 

 upon its activities to produce the shell. A special case is found in 

 Bermuda, where a land-dwelling hermit crab, Coenobita diogenes, 

 lives in the shells of Livofia pica. The remarkable fact is that Livona 

 is now extinct in Bermuda, and all the shells used by the hermits 

 are either fossils or sub-fossils; the crab relies on the products of a 



