A Gram-negative, heterotrophic, agarolytic, marine bacterium, designated strain SA1T, was isolated from a seawater sample collected in the shallow coastal region of Keelung, Taiwan. Cells were straight to slightly curved rods. Nearly all of the cells were non-motile and non-flagellated during the exponential phase of growth in broth cultures; a few cells (<1 %) were motile and were considered to have monotrichous flagella. The isolate required NaCl for growth and grew optimally at 30-35 degrees C and 2-3 % (w/v) NaCl. It grew aerobically and was incapable of anaerobic growth by fermentation of glucose or other carbohydrates. However, anaerobic growth could be achieved by reduction of nitrate to nitrite. Polar lipids comprised phosphatidylethanolamine (71.8 %), diphosphatidylglycerol (12.7 %), phosphatidylglycerol (12.2 %) and phosphatidylserine (3.3 %). Isoprenoid quinones consisted of Q-10 (87.5 %), MK-9 (6.6 %) and MK-7 (5.9 %). Major cellular fatty acids were C16 : 1 omega 7c and/or iso-C15 : 0 2-OH (28.6 %), C17 : 1 omega 8c (22.8 %), C16 : 0 (14.5 %), C18 : 1 omega 7c (11.0 %) and C17 : 0 (6.4 %). The DNA G+C content was 55.6 mol%. Phylogeny based on 16S rRNA gene sequence analysis showed that strain SA1T formed a distinct lineage within the class Gammaproteobacteria. Strain SA1T was related most closely to Teredinibacter turnerae, Cellvibrio spp., Saccharophagus degradans, Pseudomonas spp. and Microbulbifer spp., strains of these species sharing <93 % 16S rRNA gene sequence similarity with strain SA1T. The phylogenetic data and those from physiological, morphological and chemotaxonomic characterizations indicated that strain SA1T represents a novel species and genus, for which the name Simiduia agarivorans gen. nov., sp. nov. is proposed. The type strain is SA1T (=BCRC 17597T=JCM 13881T).