Seven-arm octopus


The seven-arm octopus is one of the two largest known species of octopus; based on scientific records, it has a maximum estimated total length of and mass of. The only other similarly large extant species is the giant Pacific octopus, Enteroctopus dofleini.
The genera Alloposina Grimpe, 1922, Alloposus Verrill, 1880 and Heptopus Joubin, 1929 are junior synonyms of Haliphron, a monotypic genus in the monotypic family Alloposidae, part of the superfamily Argonautoidea in the suborder Incirrata of the order Octopoda.

Description

The seven-arm octopus is so named because in males, the hectocotylus is coiled in a sac beneath the right eye. Due to this species' thick, gelatinous tissue, the arm is easily overlooked, giving the appearance of just seven arms. However, like other octopuses, it actually has eight.

Distribution

The type specimen of H. atlanticus was collected in the Atlantic Ocean at . It is deposited at the University of Copenhagen Zoological Museum.
Since then, several specimens have been caught throughout the Atlantic, as far as the Azores archipelago and near South Georgia Island.
In 2002, a single specimen of giant proportions was caught by fishermen trawling at a depth of 920 m off the eastern Chatham Rise, New Zealand. This specimen, the largest of this species and of all octopuses, was the first validated record of Haliphron from the South Pacific. It had a mantle length of, a total length of, and a weight of, although it was incomplete.

Ecology

Isotopic, photographic and video evidence have shown complex interactions between H. atlanticus and jellyfish and other gelatinous zooplankton, from feeding to protection, respectively.
Predators of H. atlanticus include the blue shark, Hawaiian monk seal, sperm whale, and swordfish.

Beak morphology