Strain ISS155^T, isolated from surface Mediterranean seawater, has cells that are Gram-reaction-negative, motile, strictly aerobic chemoorganotrophic, oxidase-positive, unable to reduce nitrate to nitrite, and able to grow with cellulose as the sole carbon and energy source. It is mesophilic, neutrophilic, slightly halophilic and has a requirement for sodium and magnesium ions. Its 16S rRNA gene sequence places the strain among members of Cellvibrionaceae , in the Gammaproteobacteria , with Agarilytica rhodophyticola 017^T as closest relative (94.3 % similarity). Its major cellular fatty acids are C_{18 : 1}, C_{16 : 0} and C_{16 : 1}; major phospholipids are phosphatidyl glycerol, phosphatidyl ethanolamine and an unidentified lipid, and the major respiratory quinone is Q8. The genome size is 6.09 Mbp and G+C content is 45.2 mol%. A phylogenomic analysis using UBCG merges strain ISS155^T in a clade with A. rhodophyticola , Teredinibacter turnerae , Saccharophagus degradans and Agaribacterium haliotis type strain genomes, all of them possessing a varied array of carbohydrate-active enzymes and the potential for polysaccharide degradation. Average amino acid identity indexes determined against available Cellvibrionaceae type strain genomes show that strain ISS155^T is related to them by values lower than 60 %, with a maximum of 58 % to A. rhodophyticola 017^T and 57 % to T. turnerae T7902^T and S. degradans 2-40^T. These results, together with the low 16S rRNA gene sequence similarities and differences in phenotypic profiles, indicate that strain ISS155^T represents a new genus and species in Cellvibrionaceae , for which we propose the name Thalassocella blandensis gen. nov., sp. nov., and strain ISS155^T (=CECT 9533^T=LMG 31237^T) as the type strain.