Three new species of the stygobiotic genus Seborgia (Amphipoda, Sebidae) are described from anchialine waters on the Loyalty Islands and on Vanuatu (Melanesia), and from slightly brackish groundwaters in the Gulf of Tonkin (Vietnam). Seborgia sanctensis n. sp. displays a biramous third uropod, a feature never previously reported in sebids. The same species is also noteworthy in having a bilobed maxilla, a trait currently regarded as diagnostic of the Sebinae. Even though these features could be interpreted as evidence supporting the establishment of a separate, new genus for this taxon, its overall similarity with the other Seborgia species is striking, and we prefer to consider it as the representative of the genus exhibiting the most plesiomorphic character states. The other Seborgia species display a relatively derived, regressive condition in both of these characters. The biramous third uropod of Seborgia sanctensis n. sp., the posterior part of the body strongly reflexed beneath the pereion when alive, the fusion of the basis segments of the paired maxillipeds in S. kanaka n. sp., and the entire telson, all lend additional support to previous suggestions that the sebids should be included among the leucothoideans. The discovery of Seborgia sanctensis n. sp. and S. kanaka n. sp., two species retaining the visual apparatus or at least traces of it, in anchialine pools located on coarse non-consolidated sediments suggests that this type of crevicular habitat is the primary habitat for the genus, and leads us to infer that Seborgia has probably come to occupy inland subterranean habitats by way of marine regressions.
Crustacea, Amphipoda, Gammaridea, Seborgia, anchialine caves, Tethyan distributions, biogeography, Loyalty Islands, Lifou, Vanuatu, Espíritu Santo, new species.