| abstract | The rheophilous forms of a collection of South-American water-mites are studied. The material of the analysis has been mainly collected in the Southern Andes, this region being the only part in South-America, which still has been "terra incognita" in the hydracarinologian sense until today. 30 new species, 13 new genra and 5 new subfamilies are described. Totally 45 species are treated.
The systematical study forms the basis for presenting the history of distribution of the rheophilous Hydrachnellae in South-America. As mites ar usually of a high geological age and rheophilous freshwater organisms generally of a very slow velocity of distribution, the todayʼs existence of a species of rheophilous Hydrachnellae can reflect very old geographical relations and connections, dating back to the Paleozoic Period. So it is possible to enumerate a series of endemic southhemispherian groups, which, to judge after their disjunct distribution, had been spread all over the southern continent that existed till the beginning of the Trias Peiod (Gondwanaland, see fig. 85). The separation between the Brazilian and the Andean district, which lasted for quite a long geological period, has led to important differences in the list of species, so that it is possible to divide South-America by the occurrence of Hydrachnellae into two main regions: The Andes and the Brazilian district (see fig. 87). The Fauna in the highland of Guiana doesnʼt seem to differ much from that of the mountainous regions of Brazil. On the other hand it is possible to speak of a northern and a southern subregion in the whole chain of the Andes. The boundary line has to be put through the desert belt of Peru and Chile, which is proofed by the existence of north-south-Andian representatives (see fig. 21).
Besides, Northern-Andes are characterized by the existence of species of holarctic families, though it is a very little number (see fig. 76). In contrast there are genera of disjunct southhemispherian distribution in the South-Andes.
Because of their systematic relationship, it can be regarded as shure, that they had their origin in the antarctic region (see fig. 66).
Of some families of the Brazilian region it is supposed that they immigrated directly from the Palearctis by means of an adequate land connection (see fig. 88). |