Summary
Sea spiders are conspicuous, and often abundant, members of the Antarctic benthic community. Nymphonidae (Pycnogonida) in Southern Ocean waters comprise over 240 species which are often diYcult to assign due to their intraspeciWc ‘highly variable’ morphology. In particular, Nymphon australe, the numerically dominant species in Antarctic waters is known to have a high level of phenotypic variation in external morphology and is also reported to have a circumpolar distribution. Circumpolarity seems contradictory to the pycnogonid’s brooding lifestyle and presumably limited dispersal. Here we examine the genetic diversity of several Nymphon species collected in the Antarctic Peninsular region. Concomitantly, we assess the genetic structure of N. australe to gain insight into Nymphon dispersal capacity. Cytochrome c oxidase subunit I (COI) and 16S ribosomal gene data suggest a recent common history and/or recent gene-Xow of N. australe populations across nearly 800 km of the Antarctic Peninsula. Furthermore, these data support that the Antarctic Peninsula region may hold two previously unrecognized species of Nymphon.