130 A BIOLOGY OF CRUSTACEA 



of the continent; the spiny lobsters, Panulirus interruptus on the 

 Pacific side, and P. argus on the Atlantic side, make a good example. 



The Pacific and Atlantic shelves of America also have their own 

 characteristic crab genera. Lophoxantlius and Pliosoma occur only 

 on the Pacific Coast, while the genera Carpoporus and Lupclla are 

 found only on the Atlantic Coast. 



The warm-water Atlantic shelf of Africa is singularly poor in 

 endemic genera of Crustacea; having only the crab Atlantollos with 

 a single species, but the number of endemic species is high. About 

 40 per cent of the West African decapod Crustacea are not found 

 elsewhere. An odd feature of the West African shelf fauna is the 

 presence of a number of genera which are otherwise characteristic 

 of the Indo-West Pacific. These genera, such as the crabs Thalamita, 

 Heteropanope and Notopus, are thought to have entered the area 

 when there was a sea connecting the Indian Ocean with the 

 Mediterranean Sea, which also had a much wider connection with 

 the Atlantic than it has at present. 



The shelf faunas of the Arctic and Antarctic seas form a marked 

 contrast with the warm-water shelf fauna. There are many fewer 

 species, but a high proportion are endemic. In the Antarctic there 

 are some 310 species of Amphipoda, and about 70 per cent of these 

 are not found elsewhere. The isopod genus Antarcturus has about 

 fourteen species, ten of which are restricted to the Antarctic. The 

 Arctic also has its endemic species; the shrimp Sclerocrangon ferox, 

 and eight of the eleven species of the amphipod genus Onisimus, 

 are confined to this region. 



Between the warm-water and polar shelves are the temperate water 

 shelves. These too have characteristic Crustacea, such as Crangon 

 allmani from the European shelf, and Oregonia gracilis which spans 

 the temperate Pacific from California to Japan. The stomatopod, 

 Squilla armata, provides an example of a widespread southern tem- 

 perate shelf species; it is found on the coasts of Chile, Cape Horn, 

 South Africa, New Zealand and South-West Australia. 



One surprising feature of the crustacean fauna of the North 

 Atlantic shelf is that a large part of it is derived from the Pacific, 

 and it can in some ways be regarded as a poorer version of the 

 North Pacific fauna. For instance, the genus Spirontocaris has 64 

 species in the two oceans; 51 of these are purely N. Pacific, 10 are 

 common to the N. Pacific and N. Atlantic, and only 3 are purely 

 N. Atlantic. Another example is given by the edible crab, Cancer, 

 which has only three species in the N. Atlantic while the N. 



