The purpleback flying squid or purpleback squid (Sthenoteuthis oualaniensis) is a species of cephalopod in the family Ommastrephidae, occurring in the Indo-Pacific. It is considered one of the most abundant large squids.

Description S. oualaniensis are sexually dimorphic where the females tend to grow larger than the males in most cases. Dimorphism differentiation occurs in the sucker ring dentition in which different sizes occur which suggests that a feeding spectrum occurs among male and female individuals. The species has a complex population structure, comprising three major and two minor forms with different morphology, anatomy, geographical distribution, and period of spawning. These forms include a giant form, a medium form with a double lateral axis on the gladius, a medium form with a single lateral axis on the gladius, a dwarf form, and a smaller earlier maturing form. The medium form is characterized by a dorsal photophore patch and fused mantle locking apparatus, it is the most common or “typical” form, and has the largest geographical distribution divide with a deeper vertical distribution when compared to the dwarf form. The dorsal mantle length (ML) of sexually mature adult males and females is 120 – 150 mm and 190 – 250 mm respectively. The smaller forms include a dwarf from an early maturing form, these two forms can be classified under the same category due to significant similarities as there is some disagreement in the literature. The smaller forms have no dorsal photophore patches and tend to reside in the equatorial waters (10 – 15 º N and S) of the Indonesian-Pacific Oceans, in which it spends the majority of its life in the upper mixed layers.