Aspects of the evolution and biogeography of stygobiontic Isopoda (Crustacea: Peracarida)

Abstract

The evolution of the stygobiontic isopods is discussed correlating the phylogenetic system with biogeography. All stygobiontic isopods probably are derived from remote marine ancestors. The colonization of subterranean aquatic biotopes occurred in two ways: (1) via the coastal groundwater in the case of the Microparasellidae, Gnathostenetroididae, Stenetriidae, and in Cyathura (Stygocyathura), (2) in most families, however, via epigean freshwater ancestors. Ancient freshwater isopods that must already have existed before the Cretaceous and whose stygobiontic phylogenetic lines partly must have existed before the opening of the Atlantic are the Aselloidea, Calabozoida, Phreatoicidea, and probably also the Protojaniridae. In the course of Cretaceous and Tertiary regressions other, more apomorphic taxa “stranded” and adapted to stygobiontic biotopes, such as the “Monolistrini” (Sphaeromatidae)