Systematics of the North American subterranean amphipod genus Bactrurus (Crangonyctidae)

Bactrurus Hay is a relatively small generic group that inhabits caves and related groundwater habitats in parts of eastern and central USA. Two field trips, conducted in the spring of 1999, yielded important new locality records that give us a better knowledge of the distribution of the genus. The examination of fresh samples as well as older collection material has resulted in descriptions of four new species. Based on these descriptions and redescriptions of three previously known species, the taxonomy of the genus is revised. In addition, a phylogenetic analysis using morphological data is employed to examine the relationship of Bactrurus to 12 selected crangonyctid taxa, including its potential sister genus Stygobromus Cope. Five epigean and hypogean amphipod taxa were chosen as outgroups for the analysis. For interspecific and intergeneric comparisons, pairwise sequence differences of the 18S (small subunit) rDNA gene are given for three species of Bactrurus and three of the outgroup taxa. Based on an updated, detailed distribution map the biogeography of Bactrurus is discussed with regard to possible dispersal and vicariant events. The evaluation of new data obtained by this study contributes to a more complete understanding of the evolutionary history of the genus.