A shiny dark yellow pigmented, Gram-stain-negative, rod-shaped, non-motile bacterium, designated as strain JC631T, was isolated from the sediment ecosystem of Chilika lagoon, India. Strain JC631T tolerates up to pH 10 and NaCl up to 3% (w/v). MK6 is the only respiratory quinone. Predominant (> 10%) cellular fatty acids are anteiso-C11:0, anteiso-C13:0, and anteiso-C15:0. Major polar lipids are phosphatidylethanolamine, phosphatidylcholine, a few unidentified phospholipids, and a few unidentified aminolipids. 16S rRNA gene sequencing showed that strain JC631T shared the highest sequence identity (98.7%) with Arenibacter latericius KMM 426T followed by Arenibacter certesii CCUG 48006T (98.6%) and other members of the genus Arenibacter (< 97%). The genome size of strain JC631T is 4.16Mb with a GC content of 40.8mol%. Strain JC631T has ANI scores of 78.3% and 78.1%; dDDH values of 22.2% and 21.8%, respectively, with the type strains of A. latericius and A. certesii. The genomic distinction is well supported by chemotaxonomic characteristics and differential physiological properties. This supports strain JC631T to be described as a new species of the genus Arenibacter, named as Arenibacter lacus sp. nov. The type strain is JC631T (= KCTC 72002T = NBRC 114071T).