Characterization of the Complete Mitochondrial Genome of Dwarf Form of Purpleback Flying Squid () and Phylogenetic Analysis of the Family Ommastrephidae.

Background: The Ommastrephidae family of cephalopods is important in marine ecosystems as both predators and prey. Species such as , , and are economically valuable but are threatened by overfishing and environmental changes. The genus , especially , shows significant morphological and genetic variation, including medium-sized and dwarf forms found in the South China Sea.

Methods: Specimens of were collected from the South China Sea, their genomic DNA sequenced, and phylogenetic relationships analyzed using mitochondrial genomes from various Ommastrephidae species.

Results: The study presents the complete mitochondrial genome of the dwarf form of (20,320 bp) and compares it with the medium-sized form, revealing a typical vertebrate structure with 13 protein-coding genes, 21 tRNA genes, and 2 rRNA genes, along with a strong AT bias. Nucleotide composition analysis shows a 12% genetic divergence between the two forms, suggesting a recent common ancestor and potential cryptic speciation, with all protein-coding genes exhibiting purifying selection based on Ka/Ks ratios below 1.

Conclusions: The mitochondrial genome of the dwarf form of shows a close evolutionary relationship with the medium-sized form and a 12% genetic divergence, suggesting potential cryptic speciation. These findings underscore the importance of mitochondrial analysis in understanding speciation and guiding future conservation efforts.