A Gram-stain-negative, non-motile and aerobic bacterial strain, designated L1 8-17T, was isolated from a marine alga, Porphyridium marinum, in South Korea. Cells of strain L1 8-17T were found to be oxidase- and catalase-positive cocci without flagella. Growth of strain L1 8-17T was observed at 20-40 °C (optimum, 37 °C), pH 6.0-10.0 (optimum, pH 7.0-8.0) and in the presence of 0-7 % (w/v) NaCl (optimum, 2-3 %). The isoprenoid quinone detected was only ubiquinone-10. Summed feature 8 (comprising C18 : 1ω7c/C18 : 1ω6c) and C16 : 0 were detected as major cellular fatty acids. The major polar lipids of strain L1 8-17T consisted of phosphatidylcholine, phosphatidylglycerol, phosphatidylethanolamine, an unidentified aminolipid, an unidentified phospholipid and an unidentified lipid. The G+C content of the genomic DNA was 59.3 mol%. Strain L1 8-17T was most closely related to Marimonas arenosa CAU 1311T, Tropicibacter naphthalenivorans C02T and Donghicola eburneus SW-277T with 96.68, 96.68 and 96.60 % 16S rRNA gene sequence similarities, respectively, but the strain formed a phylogenetic lineage clearly distinct from them within the family Rhodobacteraceae. On the basis of phenotypic, chemotaxonomic and molecular properties, strain L1 8-17T represents a novel genus of the family Rhodobacteraceae, for which the name Aquicoccus porphyridii gen. nov., sp. nov. is proposed. The type strain of the type species is L1 8-17T (KACC 18806T=JCM 31543T).