Four new species of subterranean amphipod crustaceans (Artesiidae, Hadziidae, Sebidae) from Texas, with comments on their phylogenetic and biogeographic relationships

Four new stygobiont amphipod crustaceans are described from a variety of groundwater habitats (e.g., caves, springs, interstitial media) in south-central and western Texas. The new species are Artesia welbourni (Artesiidae), Holsingerius smaragdinus (Hadziidae), Mexiweckelia hardeni (Hadziidae), and Seborgia hershleri (Sebidae). The new locality records for Artesia in Culberson County, and Holsingerius and Seborgia in Val Verde County are the first for these genera outside the artesian well in San Marcos, Texas, whereas the new record for Mexiweckelia in Medina County documents a significant range extension for this genus from north-central Mexico to south-central Texas. Seborgia relicta, previously described from the artesian well in San Marcos, is also newly recorded from Medina County. Both the phylogenetic and biogeographic implications of these new taxa are discussed at some length because they provide further insight into the origin and evolutionary biology of stygobiont crustaceans in southern Texas and northern Mexico.