A Gram-stain-negative strictly aerobic, marine bacterium, designated GH2-2^T, was isolated from a rhizosphere mudflat of a halophyte (Carex scabrifolia) in Gangwha Island, the Republic of Korea. The cells of the organism were oxidase-positive, catalase-positive, flagellated, short rods that grew at 10-40°C, pH 4-10, and 0-13% (w/v) NaCl. The predominant ubiquinone was Q-10. The major polar lipids were phosphatidylcholine, phosphatidylethanolamine, and phosphatidylglycerol. The major fatty acid is C_18:1. Phylogenetic analysis based on 16S rRNA gene sequences revealed that the novel isolate formed an independent lineage at the base of the radiation encompassing members of the genus Thioclava, except for Thioclava arenosa. The closest relatives were T. nitratireducens (96.03% sequence similarity) and T. dalianensis (95.97%). The genome size and DNA G+C content were 3.77 Mbp and 59.6 mol%, respectively. Phylogenomic analysis supported phylogenetic distinctness based on 16S rRNA gene sequences. Average nucleotide identity values were 73.6-74.0% between the novel strain and members of the genus Thioclava. On the basis of data obtained from a polyphasic approach, the strain GH2-2^T (= KCTC 62124^T = DSM 105743) represents a novel species of a new genus for which the name Hahyoungchilella caricis gen. nov., sp. nov. is proposed. Moreover, the transfer of Thioclava arenosa Thongphrom et al. 2017 to Pseudothioclava gen. nov. as Pseudothioclava arenosa comb. nov. is also proposed. Finally, Thioclava electrotropha Chang et al. 2018 is proposed to be a later heterosynonym of Thioclava sediminum Liu et al. 2017.