Five strains were isolated from moribund scallop (Pecten maximus) larvae over 5 years (1990-1995) during outbreaks of disease in a hatchery (Argenton, Brittany, France). Their pathogenic activity on scallop larvae was previously demonstrated by experimental exposure. The phenotypic and genotypic features of the strains were identical. The G + C content of the strains was in the range 39-41 mol%. DNA-DNA hybridization showed a minimum of 73% intragroup relatedness. Phylogenetic analysis of small-subunit rRNA sequences confirmed that these strains should be affiliated within the family Vibrionaceae and that they are closely related to Vibrio tapetis and Vibrio splendidus. Phenotypic and genotypic analyses revealed that the isolates were distinct from these two vibrios and so constitute a new species in the genus Vibrio. They utilized only a limited number of organic substrates as sole carbon sources, including betaine and rhamnose, but did not utilize glucose and fructose. In addition, their responses were negative for indole, acetoin, decarboxylase and dihydrolase production. The name Vibrio pectenicida is proposed for the new species; strain A365 is the type strain (= CIP 105190T).