Peculiarities of the geographical and vertical distribution of marine isopods and the problem of deep-sea fauna origin

Data on isopods processed by the author and the literature available on the subject have made it possible to provide specific lists of isopods for coastal zones of cold and cold-temperate regions in both hemispheres and for isopods from depths of more than 2000 m for the entire World Ocean. A comparative analysis shows both faunas to be very similar with respect to family and genus; in this respect they differ considerably from the shallow-water fauna of warm zones. Comparative-anatomic data indicate that the suborder Flabellifera is the most primitive, the Asellota the most specialized group; the data permit the singling out of the more primitive as well as the more specialized families in each suborder under study. Analysis of vertical distributions of all isopods in the World Ocean suggests that primitive isopods are principally confined to tropical shelves; however, in the shelves of cold and cold-temperate waters, especially in deep seas, a considerable number of phylogenetically recent families is present. Thus, the tropical shallow-water fauna proves to be the most ancient, while the shallow fauna of cold and temperate waters may be regarded as geologically more recent. The deep-sea fauna is considered to be the youngest. The author hypothesizes the probable ascendance of the deep-sea fauna from the Antarctic fauna in the period of increasing cold, as early as the late Cretaceous period. This process was promoted by glaciation in the Antarctic Ocean, and its gradual isostatic dipping together with the shelf.