Two strains, designated GCR0103(T) and GYR3121(T), were isolated from seawater of the Saemangeum Embankment in Jeollabuk-do, Korea. The cells of the two strains were Gram-reaction-negative and non-motile, and formed multicellular filaments. The colonies of the two strains were pink-pigmented and able to grow at 15-37 °C (optimum 25 °C) on R2A and NA medium. Strains GCR0103(T) and GYR3121(T) grew at pH 6.5-10 (optimum pH 7.5) and pH 5.5-9.5 (optimum pH 7.5), and within NaCl ranges of 0-0.4% and 0-1%, respectively. The polar lipid profiles of the two strains contained phosphatidylethanolamine, five unknown aminolipids, an unknown phospholipid and four or five unknown lipids. The DNA G+C contents of strains GCR0103(T) and GYR3121(T) were 56.0 and 54.5 mol%, respectively. The respiratory quinone detected in both strains was MK-7. The 16S rRNA gene sequence similarity between GCR0103(T) and GYR3121(T) was 95.5 %. The 16S rRNA gene sequence similarities of the two strains to closely related reference strains were less than 89 %. Phylogenetic analysis based on 16S rRNA genes showed that GCR0103(T) and GYR3121(T) formed a distinct phyletic line in the family Cytophagaceae. On the basis of the phenotypic, chemotaxonomic and phylogenetic properties, strains GCR0103(T) and GYR3121(T) represent two novel species in a new genus within the family Cytophagaceae, for which the names Nibrella saemangeumensis gen. nov., sp. nov. and Nibrella viscosa sp. nov. are proposed. The type strain of Nibrella saemangeumensis is GCR0103(T) ( = KACC 16453(T) = JCM 17927(T)) and the type strain of Nibrella viscosa is GYR3121(T) ( = KACC 16447(T) = JCM 17925(T)).