CHINESE MITTEN CRAB — PANNING 363 



fields near the coast and that farther inland it lives only in the rivers. 

 The species oiEriocheir leptognathus described by Dr. Mary J. Rathbun 

 inhabits China from the province of Fokin in the south, where it is 

 very rare, to the Liaotung peninsula on the Yellow Sea in the north. 

 Its principal habitat is north of Shanghai (fig. 1). 



The mitten crab belongs to the Grapsoid family group which is 

 phylogenetically the newest group of the brachyuran crustaceans. 

 The Grapsoid crabs are animals of the Tropics, but a few forms reach 

 into the Temperate Zone, and the mitten crab is one of them. Thus 

 it happens that we see characteristics in an animal living in the Tem- 

 perate Zone which really belong only to animals living in the Topics. 

 The Grapsoid crabs are marine animals, and it is an outstrnding 

 characteristic of all marine crabs that larvae escape from thear eggs 

 to drift free and pass through various stages before settling ion the 

 bottom. Thereby they differ fundamentally from all real fresh-water 

 crabs which do not go through these stages when the larvae drift, 

 about free. A whole group of Grapsoid crabs spend their adolescence 

 in brackish or fresh water where they find especially rich feeding 

 However, that is the only time they do live in brackish or fresh water. 

 They must always breed in the ocean. The larvae escape from the 

 egg in the ocean and pass through the free-drifting larval stages in salt 

 or brackish water, but however far they may venture into fresh water 

 they must always return to the ocean for reproduction. The Grap- 

 soid crabs, therefore, prefer regions close to the coast when they seek 

 fresh water. Our mitten crab belongs to this group. 



HOW THE MITTEN CRAB WAS BROUGHT INTO GERMANY 



The mitten crabs live in the Temperate Zone in eastern Asia up into 

 the far north. This fact has made possible their transfer to temperate 

 Central Europe and to cold-temperate northern Europe. Their 

 presence in Germany was probably made possible because of their 

 reproduction through free-drifting larvae brought to Germany on 

 commercial vessels. When the ships happened to fill their ballast 

 water tanks in central or north Chinese ports during the larvae's 

 spawning time, the 1.7- to 5-mm larvae of the mitten crab would, of 

 course, get into the tanks, and again when the tanks were emptied in 

 the German port the young mitten crabs, a few millimeters long, into 

 which the larvae had developed during the trip, would, of course, get 

 into one of the German rivers emptying into the North Sea. This could 

 go on unnoticed year after year. They were undoubtedly brought 

 in long ago. The first Chinese mitten crab, a large male, was dis- 

 covered in the Aller, a tributary to the Weser, in 1912. One can thus 

 consider that these crabs were first brought in during the first decade 

 of this century, and their entry therefore coincides to a certain extent 



