A novel bacterial strain, designated a4T, isolated from a sea anemone (Aiptasia pulchella) in Taiwan, was characterized using a polyphasic taxonomic approach. Strain a4T was aerobic, Gram-negative, pale-yellow-pigmented and rod-shaped. It grew optimally at 30-35 degrees C, in the presence of 3-4 % (w/v) NaCl and at pH 8.0. Phylogenetic analyses based on 16S rRNA gene sequences showed that the strain belonged to the genus Tenacibaculum (family Flavobacteriaceae, phylum Bacteroidetes). The closest neighbours were Tenacibaculum lutimaris TF-26T (97.6 % similarity) and Tenacibaculum aestuarii SMK-4T (97.7 % similarity). The novel isolate could be distinguished from all Tenacibaculum species by several phenotypic characteristics. The major fatty acids were summed feature 3 (comprising C16 : 1 omega 7c and/or iso-C15 : 0 2-OH, 19.6 %), iso-C15 : 0 (12.9 %), iso-C16 : 0 3-OH (10.2 %), iso-C17 : 0 3-OH (9.9 %) and iso-C15 : 1 (9.5 %). The DNA G+C content was 35.0 mol%. Hence, genotypic and phenotypic data demonstrate that strain a4(T) should be classified as a representative of a novel species in the genus Tenacibaculum, for which the name Tenacibaculum aiptasiae sp. nov. is proposed. The type strain is a4T (=BCRC 17655T =LMG 24004T).