Species of the genus Pseudoalteromonas are frequently isolated from marine ecosystems and appear to be particularly abundant in Antarctic coastal waters. Most Pseudoalteromonas strains isolated form sea ice and underlying seawater samples are phenotypically similar to the species Pseudoalteromonas antarctica and Pseudoalteromonas nigrifaciens. However, a minority of isolates were recognized by phenotypic, DNA-DNA hybridization and 16S rRNA-based phylogenetic studies to represent a distinct genospecies clustering at the periphery of the non-pigmented, Pseudoalteromonas species clade. These strains are non-pigmented, halotolerant psychrotrophs that are capable of hydrolysing starch and chitin, and possess a DNA G+C content of 38-39 mol%. It is proposed that this group represents a novel species, Pseudoalteromonas prydzensis sp. nov., for which the type strain is ACAM 620(T).