ABSTRACT
The subterranean amphipod fauna of North America is highly diverse and presently includes 169 species representing 28 genera in 10 families or family groups. The vast majority of these species are stygobionts (i.e. obligate dwellers in aquatic subterranean habitats). Three major zoogeographic patterns are recognized among subterranean amphipods in North America: (1) ancient freshwater distribution; (2) marine relict distribution; and (3) marine-brackish water distribution. Taxa with pattern 1 distribution are exclusively freshwater forms restricted to the Holarctic region and have no known marine relatives. The large, exclusively subterranean genus Stygobromus (Crangonyctidae) is a principal example. Taxa with pattern 2 distribution are exclusively freshwater forms but have close relatives in marine/brackish water and are believed to have been derived from marine ancestors by stranding during marine transgressions in Late Cretaceous and Tertiary times. The weckeliid group of Hadziidae is a principal example. Taxa with pattern 3 distribution live at present in habitats ranging from fully marine to marginally fresh waters on and around islands in the West Indies, where they are believed to have become isolated during emergence of island groups in middle to late Cenozoic times. The genus Metaniphargus (Hadziidae) is a principal example.
