BIOGEOGRAPHIC SYNTHESIS OF THE INSULAR GROUNDWATER FAUNAS OF THE (SUB)TROPICAL ATLANTIC

Anchihaline habitats occur most frequently in subsiding areas. Typical ly, they are populated by ancestors of marine origin. These ancestral forms have a much wider distribution in the open sea, thus their hypog ean descendents occur in phenetically similar populations on various i slands. On the contrary, on rising islands, marine ancestors stranded during the uplift and got isolated in brackish or fresh ground waters, giving rise to phenetic and genetic isolates in very restricted areas . They belong to old genera with a large ditribution (amphi-Atlantic o r Tethyan) The stygofaunas of both rising and subsiding areas thus ori ginated in the sea, but contrary to the often uttered suggestions, not in the deep-sea. Phenetic resemblance between deep-sea and anchihalin e taxa may indicate common ancestry, but then it must be shallow-water ancestry for both, simply because no deep-sea species survived the tw o oxygen-crises in the early and mid-Tertiary.