The genusThalassotaleais ubiquitous in marine environments, and up to 20 species have been described so far. A Gram-staining-negative, aerobic bacterium, designated strain PTE2Twas isolated from laboratory-reared larvae of the Japanese sea cucumberApostichopus japonicus. Phylogenetic analysis based on the 16S rRNA gene nucleotide sequences revealed that PTE2Twas closely related toThalassotalea sediminisN211T(= KCTC 42588T= MCCC 1H00116T) with 97.9% sequence similarity. ANI andin silicoDDH values againstThalassotaleaspecies were 68.5–77.0% and 19.7–24.6%, respectively, indicating the novelty of PTE2T. Based on genome-based taxonomic approaches, strain PTE2T(= JCM 34608T= KCTC 82592T) is proposed as a new species,Thalassotalea hakodatensissp. nov.