142 A BIOLOGY OF CRUSTACEA 



Within the genus Daphnia there has heen an interesting radiation 

 to produce lake plankton forms from different groups of the genus 

 in various parts of the world. In Europe the lake plankton species 

 helong mainlv to the D. longispina group. In North America the 

 /). pulex group has also produced a crop of lake dwellers, while in 

 Africa and Australasia the sub-genus Ctenodaphnia is responsible. 



Ostracods and copepods are also abundant in fresh water, but it 

 is difficult to make any general statement about their zoogeography. 

 The best example of a distinct fauna within these groups is found 

 in I ,ake Tanganyika. The ostracods are here represented mainly by 

 two genera with 1 1 and 8 endemic species respectively, while among 

 the copepod genera Shizopera has produced eight endemic species, 

 Eucy clops is represented by 7 species, 4 of which are endemic, and 

 Microcyclops adds another 6 endemic species. 



Although many copepods and ostracods are widespread, certain 

 areas of the earth can be characterised by endemic fresh-water 

 genera of these two groups. The copepods Orthocyclops and Penta- 

 camptus are characteristic of North America; Afrocyclops, Afro- 

 camptus, and the ostracod Afrocypris are endemic in Africa — 

 examples could be multiplied. The point is not to produce lists 

 for various localities, but to show that the ostracods and copepods 

 are by no means as cosmopolitan as was at one time thought. 



Few members of the Malacostraca have penetrated into fresh 

 waters, but their distribution is better known because they are 

 generally more conspicuous. But first there are a few inconspicuous 

 members of this group. The Spelaeogriphacea are known from a 

 single species, Spelaeogriphus lepidops, described in 1957 from caves 

 in South Africa. The Thermosbaenacea also have a couple of 

 cavernicolous species, Monodella argentarii and M. stygicolla, both 

 from Italy. Another member of this order, Thermosbaena mirabilis, 

 lives in warm water springs in Tunisia. The temperature tolerated 

 by this small creature is remarkably high, about 47 ° C. Thermos- 

 baena is remarkable in that it cannot tolerate even moderately 

 lowered temperature; it becomes moribund at 35 C, which is a 

 temperature high enough to kill most ordinary fresh-water crusta- 

 ceans. A few other Crustacea can tolerate warm water, the ostracod 

 Cypris balnearia being the most notable example. This creature can 

 live in water at 51 ° C. and disappears in places where the tempera- 

 ture falls below 40 C. 



The genus Bathynella was first found in a deep well near Prague 

 in 1882, and was not found again until 19 14. when it was discovered 



