54 A NATURAL HISTORY OF THE SEAS 



Various species allied to the Land Crab have invaded 

 fresh-waters and of late years the so-called Mitten Crab 

 (Eriocheir) has achieved a disagreeable notoriety. Originally 

 believed to have come from Japan, it is now well established 

 on the Continent, notably in the Elbe, where it does 

 much damage by tunnelling river banks. A more 

 sensational feature of the crab is the fact that it has now 

 been established that it is an intermediary host of 

 the river fluke responsible for a form of tubercle. 

 Its use as human food has, as a result, now been 

 prohibited. 



The Calling Crab (Gelasimus), widely spread over all 

 the warmer coasts, is distinguished by the huge develop- 

 ment of one of the male's claws. This feature is used for 

 fighting and also to close the mouth. It is further of 

 special sexual significance, since it is brightly coloured 

 and flourished with much ceremony for the contemplation 

 of a prospective bride. A species of Gelasimns is the 

 subject of a remarkable fishery off the coast of Portugal. 

 The fishermen simply remove the large claws of the males, 

 liberating the despoiled owners, who proceed to grow 

 fresh claws, though these never attain to the original 

 proportions. 



The Pea Crabs {Pinnotheres) constitute a strange group 

 of degenerate little crustaceans that have taken to a life of 

 commensalism. The female of our native species almost 

 invariably seeks shelter within a bivalve mollusc such as 

 an oyster or mussel, and as a result of thus refusing to 

 face the bufferings of chance its carapace has become 

 membraneous, whilst the limbs have dwindled and become 

 almost useless. The male, however, remains active and 



