Two marine, heterotrophic, aerobic, pigmented and gliding bacteria, isolated from the sea urchin Strongylocentrotus intermedius were subjected to a polyphasic taxonomy study. The 16S rRNA gene sequence analysis revealed that strains KMM 6032T and KMM 6047 formed a distinct branch within the genus Arenibacter, a member of the family Flavobacteriaceae. The level of sequence similarity between the novel isolates and members of the genus Arenibacter was 94.5-98.9%. The DNA G+C content was 39-40 mol%. The dominant fatty acids were iso-C15:1, iso-C15:0, C15:0, C15:1omega6c, iso-C15:0 3-OH, iso-C17:1omega9c, iso-C17:0 3-OH and summed feature 3 (comprising iso-C15:0 2-OH and/or C16:1omega7c). The results of DNA-DNA hybridization experiments supported by phenotypic data indicated that the isolates represent a novel species within the genus Arenibacter, for which the name Arenibacter echinorum sp. nov. is proposed. The type strain is KMM 6032T (=KCTC 22013T=LMG 22574T).