Two extremely halophilic archaea, strains RO5-2(T) and RO5-14, were isolated from Rudong marine solar saltern in Jiangsu, China. Cells of the two strains were pleomorphic, motile and stained Gram-negative. Colonies were red-pigmented. Strains RO5-2(T) and RO5-14 were able to grow at 20-50 degrees C (optimum 37 degrees C), at 2.6-4.8 M NaCl (optimum 3.4-3.9 M NaCl), at 0.03-0.7 M MgCl(2) (optimum 0.5 M MgCl(2)) and at pH 5.5-8.0 (optimum pH 6.5-7.0). Cells lyse in distilled water and the minimal NaCl concentration to prevent cell lysis was 12 % (w/v). The major polar lipids of the two strains were phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester and two major glycolipids chromatographically identical to sulfated mannosyl glucosyl diether (S-DGD-1) and mannosyl glucosyl diether (DGD-1). The 16S rRNA gene sequences of strains RO5-2(T) and RO5-14 showed 93.4-93.8 % similarity to the closest cultivated relative, Halosarcina pallida. The DNA G+C content of strains RO5-2(T) and RO5-14 was 61.0 mol% and 59.9 mol%, respectively. The DNA-DNA relatedness between strains RO5-2(T) and RO5-14 was 86.0 %. The phenotypic, chemotaxonomic and phylogenetic properties suggest that strains RO5-2(T) and RO5-14 represent a novel species in a new genus within the family Halobacteriaceae, for which the name Halopelagius inordinatus gen. nov., sp. nov. is proposed. The type strain is RO5-2(T) (=CGMCC 1.7739(T) =JCM 15773(T)).