The core of the Vibrio Harveyi clade contains V. harveyi, V. campbellii, V. owensii, V. jasicida, and V. rotiferianus. They are well recognized aquatic animal pathogens, but misclassification has been common due to similarities in their rDNA sequences and phenotypes. To better understand their evolutionary relationships and functional features, we sequenced a shrimp pathogen strain V. harveyi 1114GL, reclassified it as V. campbellii and compared this and 47 other sequenced Vibrio genomes in the Harveryi clade. A phylogeny based on 1,775 genes revealed that both V. owensii and V. jasicida were closer to V. campbellii than to V. harveyi and that V. campbellii strains can be divided into two distinct groups. Species-specific genes such as intimin and iron acquisition genes were identified in V. campbellii. In particular, the 1114GL strain contains two bacterial immunoglobulin-like genes for cell adhesion with 22 Big_2 domains that have been extensively reshuffled and are by far the most expanded among all species surveyed in this study. The 1114GL strain differed from ATCC BAA-1116 by ~9% at the synonymous sites, indicating high diversity within V. campbellii. Our study revealed the characteristics of V. campbellii in the Harveyi clade and the genetic basis for their wide-spread pathogenicity.