Longest mantle for an octopus

In octopuses, the mantle is every part of the body visible behind the head and tentacles, and includes in deep-sea species any external fins that may be present. The octopus species with the longest mantle (and therefore the longest body, per se) is the seven-arm octopus Haliphron atlanticus, whose maximum body length is 0.69 m (recorded from a huge specimen captured in 2002 off New Zealand's eastern Chatham Rise in the South Pacific), as compared with 0.6 m for the Pacific giant octopus Enteroctopus dofleini, which is heavier and bulkier, but slightly shorter.

The reason why this very sizeable species is called the seven-arm octopus is that in the male, one of its eight tentacles (known as the hectocotylus) is very small and specialized, used specifically in egg fertilisation and hidden away in a sac beneath its right eye. Consequently, it is not readily noticed, giving many observers the false impression that this octopus only possesses seven tentacles instead of the customary eight for octopuses.