We report an entoproct epibiotic on the surface of a sea spider (Pycnogonida). The pycnogonid was identified as Nymphon sp. (Nymphonidae). The entoproct was colonial, with three zooids, and was identified both morphologically and by a molecular phylogeny as Barentsia sp. (Barentsiidae). The largest zooid had eight tentacles and was about 0.7 mm long, smaller than for most colonial entoproct species. We determined partial sequences for the 18S rRNA and 28S rRNA genes from the entoproct. In an 18S-based maximum likelihood tree (1507 characters), the entoproct was the sister taxon to Barentsia gracilis.