Squid taxonomy leans on hard parts and body proportions, and bigfin reef squid across the Indo-Pacific look broadly alike. Japanese fishers, however, had long distinguished several forms by egg capsule shape, breeding season and body size, and referred to them by separate local names.
Molecular work confirmed the fishers. At least three genetically distinct lineages occur in Japanese waters, overlapping geographically without evidence of gene flow, and further divergent lineages have been reported elsewhere in the Indo-Pacific range. The name Sepioteuthis lessoniana therefore covers a species complex rather than one species, and figures published for growth, lifespan and fecundity under that name may combine different animals.
The practical effect is on management. A fishery managed as one stock may in fact be several stocks with different growth rates and spawning seasons. Formal descriptions have not been completed for all the lineages, so the number of species in the complex is unsettled, and much of the older literature cannot be reliably assigned to any one of them.