During a study intended to screen for agar-degrading bacteria, strain M2-5T was isolated from black sand off the shore of Jeju Island, Republic of Korea. Strain M2-5T exhibited agarase activity; the β-agarase gene of the isolate had 62 % amino acid sequence identity to the β-agarase gene of Microbulbifer thermotolerans JAMB A94T. The isolate was closely related to members of the genus Simiduia but was clearly discernible from reported Simiduia species, based on a polyphasic analysis. Cells of strain M2-5T were Gram-negative, catalase- and oxidase-positive, motile rods. The DNA G+C content was 53.3 mol%. The predominant isoprenoid quinone was Q-8. The major cellular fatty acids were C17:1ω8c (25.9 %), summed feature 3 (iso-C(15 : 0) 2-OH and/or C16:1ω7c; 17.2 %) and C17:0 (15.0 %). Phylogenetic analysis using 16S rRNA gene sequences showed that strain M2-5T had 96.6 % gene sequence similarity to Simiduia agarivorans SA1T, the most closely related type strain of the genus Simiduia. These results suggest that strain M2-5T represents a novel species in the genus Simiduia, for which the name Simiduia areninigrae sp. nov. is proposed; the type strain is M2-5T (=KCTC 23293T=NCAIM B 02424T).