A rod shaped, Gram-stain-negative, chemo-organotrophic, heterotrophic, strictly aerobic, non-gliding bacterium, designated strain PLR(T), was isolated from faeces of the mollusc Aplysia punctata (Mollusca, Gastropoda) that had been fed with green algae belonging to the genus Ulva. The novel strain was able to degrade ulvan, a polysaccharide extracted from green algae (Chlorophyta, Ulvophyceae). The taxonomic position of strain PLR(T) was investigated by using a polyphasic approach. Strain PLR(T) was dark orange, oxidase-positive, catalase-positive and grew optimally at 25 °C, at pH 7.5 and in the presence of 2.5 % (w/v) NaCl with an oxidative metabolism using oxygen as the electron acceptor. Nitrate could not be used as the electron acceptor. Strain PLR(T) had a Chargaff's coefficient (DNA G+C content) of 35.3 mol%. Phylogenetic analysis based on the sequence of the 16S rRNA gene placed the novel strain in the family Flavobacteriaceae (phylum 'Bacteroidetes'), within a clade comprising Stenothermobacter spongiae, Nonlabens tegetincola, Sandarakinotalea sediminis, Persicivirga xylanidelens and Persicivirga dokdonensis. The closest neighbours of strain PLR(T) were P. xylanidelens and P. dokdonensis, sharing 95.2 and 95.5 % 16S rRNA gene sequence similarity, respectively. Phylogenetic inference and differential phenotypic characteristics demonstrated that strain PLR(T) represents a novel species of the genus Persicivirga, for which the name Persicivirga ulvanivorans sp. nov. is proposed. The type strain is PLR(T) ( = CIP 110082(T) = DSM 22727(T)).