Seven-arm octopus

Seven-armed octopus
Ventral view of young female (70 mm ML)
Lateral view of young male
Scientific classification
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Order: Octopoda
Superfamily: Argonautoida
Family: Alloposidae
Verrill, 1881
Genus: Haliphron
Steenstrup, 1861
Species: H. atlanticus
Binomial name
Haliphron atlanticus
Steenstrup, 1861
Synonyms
  • Alloposus mollis
    Verrill, 1880
  • ?Octopus alberti
    Joubin, 1895
  • Alloposus pacificus
    Ijima & Ikeda, 1902
  • Heptapus danai
    Joubin, 1929
  • Alloposus hardyi
    Robson, 1930
  • ?Alloposina albatrossi
    Robson, 1932

The seven-arm octopus or septipus (Haliphron atlanticus) is one of the two largest known species of octopus; based on scientific records, it has a maximum estimated total length of 3.5 m (11 ft) and mass of 75 kg (165 lb).[1][2] The only other similarly large extant species is the giant Pacific octopus, Enteroctopus dofleini.

The genera Alloposina Grimpe, 1922, Alloposus Verrill, 1880 and Heptapus Joubin, 1929 are junior synonyms of Haliphron.

Description

Egg string and embryos of H. atlanticus collected north of the Cape Verde Islands (17°24′N 22°57′W / 17.400°N 22.950°W / 17.400; -22.950). The eggs measure around 8 mm at their widest.

The seven-arm octopus is so named because in males the hectocotylus (a specially modified arm used in egg fertilization) 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 38°N 34°W / 38°N 34°W / 38; -34. It is deposited at the Zoologisk Museum, University of Copenhagen.[3]

Since then, several specimen have been caught throughout the Atlantic, as for the Azores arquipelago[4] and near South Georgia Island[5].

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 octopodes, was the first validated record of Haliphron from the South Pacific. It had a mantle length of 0.69 m (2.3 ft), a total length of 2.90 m (9.5 ft), and a weight of 61.0 kg (134.5 lb), although it was incomplete.[1][2]

Ecology

Isotopic[5], photographic and video evidence [4] have shown complex interaction between H.atlanticus and jellyfish and other gelatinous zooplancton, from feeding to protection (respectively).

Beak morphology

Lower (left) and upper beaks of female Haliphron atlanticus (estimated 150 mm ML) in lateral view
3D red cyan glasses are recommended to view this image correctly.

See also

References

  1. 1 2 O'Shea, S. (2002). "Haliphron atlanticus — a giant gelatinous octopus" (PDF). Biodiversity Update. 5: 1.
  2. 1 2 O'Shea, S. (2004). "The giant octopus Haliphron atlanticus (Mollusca : Octopoda) in New Zealand waters". New Zealand Journal of Zoology. 31 (1): 7–13. doi:10.1080/03014223.2004.9518353.
  3. ↑ Current Classification of Recent Cephalopoda
  4. 1 2 Rosa, R.; Kelly, J.; Lopes, V.; Paula, J.; Goncalves, J.; Calado, R.; Norman, M.; Barreiros, J. (2017). "Deep-sea seven-arm octopus hijacks jellyfish in shallow waters". Marine Biodiversity. doi:10.1007/s12526-017-0767-3.
  5. 1 2 Guerreiro, M.; Phillips, R.; Cherel, Y.; Ceia, F.; Alvito, P.; Rosa, R.; Xavier, J. (2015). "Habitat and trophic ecology of Southern Ocean cephalopods from stable isotope analyses" (PDF). Marine Ecology Progress Series. 530: 119–134. doi:10.3354/meps11266.

Further reading


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