132 A BIOLOGY OF CRUSTACEA 



are compared. In the Indian Ocean about 109 species live near the 

 surface, only 9 species are found at 300 metres below the surface, 

 but the number increases to 24 at about 1,000 metres then decreases 

 again to 2 at 2,000 metres. 



Like their relatives on the deep-sea floor, the bathypelagic 

 Crustacea are often larger than their shallow-water relatives. The 

 ostracod Gigantocypris deserves its name, for it is the size of a 

 cherry, while most other members of the Ostracoda are but a 

 couple of millimetres long. Among the amphipods, Cystisoma 

 reaches a length of two inches or more while most others in the 

 group are less than half this length. 



Various bathypelagic Crustacea are limited in their distribution, 

 but it has not proved possible to define any clear-cut faunistic 

 regions. The nearest approach to a geographically defined bathy- 

 pelagic fauna is in the Arctic Sea, including the Norwegian Basin. 

 The most characteristic species of this region is the amphipod 

 Cyclocaris guilelmi. This species, and two other rarer amphipods, 

 are the only crustaceans in this rather limited fauna which do not 

 occur elsewhere. Some others of the bathypelagic Crustacea are very 

 widespread; Sergestes arcticus, which lives at a depth of 400-800 

 metres during the day, may be regarded as cosmopolitan, and the 

 large primitive mysidacean Gnathophausia gigas is found in all the 

 oceans. 



CRUSTACEA OF THE INLAND SEAS 



The inland seas gradually develop more characteristic faunas the 

 greater their isolation from the oceans. The Crustacea of the Medi- 

 terranean are not markedly different from those in the Atlantic 

 outside the Straits of Gibraltar; in fact, nearly 60 per cent of the 

 Norwegian species are found in the Mediterranean. Nevertheless it 

 can be said that there is a faunistic unit which includes the Mediter- 

 ranean and the western Atlantic from Capo Blanco to the western 

 entrance to the English Channel. A number of Mediterranean 

 Crustacea extend around the north-western coast of Africa, and 

 have their northern limits on the south-western coasts of Britain. 

 The large spider crab. Main squinado, will serve as an example. The 

 opening of the Suez Canal contributed an eastern element to the 

 Mediterranean Crustacea. Some of the crabs from the Red Sea, 

 such as Myra fugnax and Lupa ( = Neptunus) pelagica have been 

 found on the north-eastern shores of Cyprus. 



