The nematode worm Scottnema lindsayae (Cephalobidae) was found near the base of the Beardmore Glacier in the Transantarctic Mountains 83.48 degrees S, over 5 degrees further south than previously recorded. Identification was confirmed using morphological analyses of males, females and juvenile stages, and by DNA sequencing of the ITS1 region of the ribosomal RNA tandem repeat unit. These data revealed no discernable morphological or ITS rDNA sequence variation between the extreme southern population of S. lindsayae and disparate populations from the McMurdo Dry Valleys in south Victoria Land (77-78 degrees S). Based on these results, we suggest that broadcast dispersal, with accompanying high rates of gene flow, establish the extreme southern distribution of the phylum Nematoda. High abundance, low rates of diversification and lack of an apparent biogeographic structure across latitudinal and environmental gradients implies that their presence in simple Antarctic soil ecosystems is stable, so long as physical and biological controls on their distributions remain within viable parameters. Recent evidence that S. lindsayae populations are in decline suggests that their high dispersal rates are insufficient to buffer current, unfavorable environmental changes and may foreshadow longer-term ecosystem disruption.