New subterranean Sebidae(Crustacea, Amphipoda, Gammaridea)from Vietnam and SW Pacific

摘要

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 featurenever previously reported in sebids. The same species is also noteworthy inhaving a bilobed maxilla, a trait currently regarded as diagnostic of the Sebinae.Even though these features could be interpreted as evidence supporting theestablishment of a separate, new genus for this taxon, its overall similaritywith the other Seborgia species is striking, and we prefer to consider it as therepresentative of the genus exhibiting the most plesiomorphic character states.The other Seborgia species display a relatively derived, regressive condition inboth 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 thesebids should be included among the leucothoideans. The discovery of Seborgiasanctensis n. sp. and S. kanaka n. sp., two species retaining the visual apparatusor at least traces of it, in anchialine pools located on coarse non-consolidatedsediments suggests that this type of crevicular habitat is the primary habitatfor the genus, and leads us to infer that Seborgia has probably come to occupyinland subterranean habitats by way of marine regressions.