PARASITES AND MESSMATES 215 



footed worms {Nereilepas fucata), which may some- 

 times be observed to protrude its head from the 

 shell when the Crab is feeding, and to snatch away 

 fragments of the prey from the very jaws of its host. 

 It is thus, in the strict sense of the word, a com- 

 mensal. Species of Copepods, Amphipods, Porce- 

 lain Crabs, and even a Mysid, have been found 

 sharing the lodging of Hermit Crabs in a similar 

 way, and in addition there are various parasites, 

 presently to be mentioned, found on the Crabs 

 themselves, so that each Crab forms the centre of a 

 whole community of widely diverse organisms all 

 more or less directly dependent on it. 



A habit similar to those of some Hermit Crabs is 

 that of the Crab Droniia (see Plate IX.), mentioned 

 in a previous chapter, which carries, as a cloak, 

 a mass of living sponge, holding it in position by 

 means of the last two pairs of legs. Even the 

 "masking" habit of the Spider Crabs, already 

 described (p. g6), may be regarded as a kind of 

 symbiosis, since the sponges, zoophytes, etc., which 

 grow on the Crabs no doubt benefit by being carried 

 about in return for the protection they give. 



One of the strangest habits is that of certain little 

 tropical Crabs, of which Melia tessellata (Fig. 68) is 

 the best known, which carry in each claw a living 

 Sea-anemone and use it as a weapon. The claws or 

 chelipeds are in this case of small size, so that they 

 woud be of little use by themselves for attack or 



