A novel Gram-stain-negative, strictly aerobic, rod-shaped motile bacterium with a single flagellum, designated strain WRAS1T, was isolated from deep seawater of the Okinawa Trough. Growth occurred in the presence of 0.0-9.0 % NaCl (w/v; optimum, 3.0-4.0 %), at 4-45 °C (optimum, 28-37 °C) and pH 7.0-10.0 (optimum, pH 7.0-8.0). The major fatty acid (>10 % of total fatty acids) was summed feature 8, comprising C18:1ω6c and/or C18:1ω7c. The major polar lipids were phosphatidylcholine, phosphatidylglycerol, phosphatidylethanolamine and three unidentified lipids. The major respiratory quinone was ubiquinone-10. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain WRAS1T was in the genus Thalassococcus and showed the highest 16S rRNA gene sequence similarity of 97.5 % to Thalassococcus halodurans JCM13833T. Genome relatedness between strain WRAS1T and T. halodurans JCM13833T was computed using both average nucleotide identity and DNA-DNA hybridization with values of 74.11 % and 22.70±2.3 %, respectively. The genomic DNA G+C content calculated from the genome sequence of strain WRAS1T was 65.6 %. On the basis of polyphasic analyses, strain WRAS1T is considered to represent a novel species in the genus Thalassococcus, for which the name Thalassococcusprofundi sp. nov. is proposed. The type strain is WRAS1T (=CGMCC 1.16123T=MCCC 1K03253T =KCTC 52696T).