An agar-degrading bacterium, designated as strain G7(T), was isolated from a coastal seawater sample from Gaya Island (Gayado in Korean), Republic of Korea. The isolated strain G7(T) is gram-negative, rod shaped, aerobic, non-motile, and non-pigmented. A similarity search based on its 16S rRNA gene sequence revealed that it shares 95.5%, 90.6%, and 90.0% similarity with the 16S rRNA gene sequences of Catenovulum agarivorans YM01(T), Algicola sagamiensis, and Bowmanella pacifica W3-3A(T), respectively. Phylogenetic analyses demonstrated that strain G7(T) formed a distinct monophyletic clade closely related to species of the family Alteromonadaceae in the Alteromonas-like Gammaproteobacteria. The G+C content of strain G7(T) was 41.12 mol%. The DNA-DNA hybridization value between strain G7(T) and the phylogenetically closest strain YM01(T) was 19.63%. The genomes of G7(T) and YM01(T) had an average ANIb value of 70.00%. The predominant isoprenoid quinone of this particular strain was ubiquinone-8, whereas that of C. agarivorans YM01(T) was menaquinone-7. The major fatty acids of strain G7(T) were Iso-C15:0(41.47%), Anteiso-C15:0(22.99%), and C16:1ω7c/iso-C15:02-OH (8.85%), which were quite different from those of YM01(T). Comparison of the phenotypic characteristics related to carbon utilization, enzyme production, and susceptibility to antibiotics also demonstrated that strain G7(T) is distinct from C. agarivorans YM01T. Based on its phenotypic, chemotaxonomic, and phylogenetic distinctiveness, strain G7(T) was considered a novel genus and species in the Gammaproteobacteria, for which the name Gayadomonas joobiniege gen. nov. sp. nov. (ATCC BAA-2321 = DSM25250(T) = KCTC23721(T)) is proposed.