---

Polychaetes are ecologically important in the food chain, and also vital in ecosystem monitoring and environmental stress assessment. In the current study, sequence variation in a segment of COI gene sequencing by mitochondrial DNA barcoding and comparing nucleotide divergence was employed for molecular analysis of Perinereis polychaetes (Nereididae). Analysis of 50 sequenced specimens, representing 39 new sequences, and 11 sequences with 100 percent similarity with GenBank records, which revealed 1.8 times more sequence divergence between than within species (1.96 versus 3.52%). Phylogenetic analysis data indicated that maximum divergence within barcode clusters increased by the number of specimens. The phylogeny also suggests that most of the identified Perinereis species in this research showed low genetic relationship towards similar species from other world regions. Assessment of genetic similarity rate showed that Perinereis polychaetes in Bushehr province were highly similar, while Perinereis polychaetes in Bandar Abbas were less similar to Bushehr Perinereis polychaetes, the observed divergence was mostly at subspecies level and it can be concluded that in terms of species structure, Perinereis polychaetes of Deylam, Bushehr, Dayyer and Bandar Abbas, showed low genetic divergence.