As part of a study carried out for detecting Arcobacter spp. in shellfish, three mussel isolates that were Gram-negative slightly curved rods, non-spore forming, showed a new 16S rDNA-RFLP pattern with a specific identification method for the species of this genus. Sequences of the 165 rRNA gene and those of the housekeeping genes rpoB, gyrB and hsp60 provided evidence that these mussel strains belonged to an unknown genetic lineage within the genus Arcobacter. The similarity between the 16S rRNA gene sequence of the representative strain (F79-6(T)) and type strains of the other Arcobacter species ranged between 94.1% with A. halophilus and 99.1% with the recently proposed species A. defluvii (CECT 7697(T)). DDH results between strain F79-6(T) and the type strain of the latter species were below 70% (53 +/- 3.0%). Phenotypic characteristics together with MALDFTOF mass spectra differentiated the new mussel strains from all other Arcobacter species. All the results indicate that these strains represent a new species, for which the name Arcobacter ellisii sp. nov. with the type strain F79-6(T) (=CECT 7837(T) = LMG 26155(T)) is proposed. (C) 2011 Elsevier GmbH. All rights reserved.