Opisthoteuthis extensa
Insigniteuthis extensa is a species of flapjack octopus from waters off Indonesia and north-western Australia.
The species was originally described from a single female specimen captured in 1899 off the west coast of Sumatra, at 768 m depth. The relatively basic original description rendered the species difficult to distinguish from others in the genus, with some authors even proposing similarity with Opisthoteuthis pluto.
The species was recently redescribed by re-examination of the type specimen and three additional specimens, two mature males from near the type locality, and another from off northwestern Australia, depth range 694–1073 m.
The species has up to 80 suckers per arm, mature males have a 'distal enlarged sucker field', a region with 4 enlarged suckers on each of arm pairs III and IV. The species also has multiple 'web nodules' along the ventral edge of each arm. Internally with 6 or 7 lamellae on each gill, and with the shell and reproductive systems having more subtle differences relative to other species. The configuration of enlarged suckers was found to be very similar to Insigniteuthis dongshaensis from the South China Sea.