Seven-arm octopus explained

The seven-arm octopus (Haliphron atlanticus), also known as the blob octopus or sometimes called septopus, is one of the two largest known species of octopus; the largest specimen ever discovered had an estimated total length of 3.5m (11.5feet) and mass of 75kg (165lb).^{[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 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 (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 (west of the Azores). It is deposited at the University of Copenhagen Zoological Museum.^[3]

Since then, several specimens have been caught throughout the Atlantic, as far as the Azores archipelago^[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 octopuses, was the first validated record of Haliphron from the South Pacific. It had a mantle length of 0.69m (02.26feet), a total length of 2.9m (09.5feet), and a weight of 61kg (134lb), although it was incomplete.

Ecology

Isotopic, photographic and video evidence^[4] 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.^{[6] [7] [8] [9] [10]}

See also

• Cephalopod size

Further reading

• Bakken, T. & T. Holthe 2002. Haliphron atlanticum (Cephalopoda, Alloposidae) caught in Skorafjorden (64°N), Norway. Fauna norv. 22: 37–38.
• Willassen . E . 1986 . Haliphron atlanticus Steenstrup (Cephalopoda: Octopoda) from the coast of Norway . Sarsia . 71 . 35–40 . 10.1080/00364827.1986.10419671.

External links

• Tree of Life web project: Haliphron atlanticus
• The giant octopus Haliphron atlanticus (Mollusca: Octopoda) in New Zealand waters
• BBC News: Giant octopus puzzles scientists
• Tony Wu Underwater Photography: Seven-arm octopus

Notes and References

1. O'Shea . S. . 2002 . Haliphron atlanticus — a giant gelatinous octopus . Biodiversity Update . 5 . 1 .
2. O'Shea . S. . 2004 . The giant octopus Haliphron atlanticus (Mollusca : Octopoda) in New Zealand waters . 10.1080/03014223.2004.9518353 . New Zealand Journal of Zoology . 31 . 1. 7–13 . 84954869 . free .
3. http://www.mnh.si.edu/cephs/newclass.pdf Current Classification of Recent Cephalopoda
4. 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 . 10.1007/s12526-017-0767-3 . Marine Biodiversity . 49. 495–499 . 255616524 .
5. 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 . 10.3354/meps11266 . Marine Ecology Progress Series . 530 . 119–134 . 2015MEPS..530..119G . free .
6. Henderson . A. C. . Flannery . K. . Dunne . J. . Observations on the biology and ecology of the blue shark in the North-east Atlantic . Journal of Fish Biology . May 2001 . 58 . 5 . 1347–1358 . 10.1111/j.1095-8649.2001.tb02291.x.
7. Goodman-Lowe . G. D. . Diet of the Hawaiian monk seal (Monachus schauinslandi) from the Northwestern Hawaiian islands during 1991 to 1994 . Marine Biology . 29 October 1998 . 132 . 3 . 535–546 . 10.1007/s002270050419. 84310964 .
8. Chua . Marcus A.H. . Lane . David J.W. . Ooi . Seng Keat . Tay . Serene H.X. . Kubodera . Tsunemi . Diet and mitochondrial DNA haplotype of a sperm whale (Physeter macrocephalus) found dead off Jurong Island, Singapore . PeerJ . 5 April 2019 . 7 . e6705 . 10.7717/peerj.6705. 6452849 . 30984481 . free .
9. Clarke . M.R. . Pascoe . P.L. . Cephalopod Species in the Diet of a Sperm Whale (Physeter Catodon) Stranded at Penzance, Cornwall . Journal of the Marine Biological Association of the United Kingdom . 11 May 2009 . 77 . 4 . 1255 . 10.1017/S0025315400038819. 86637228 .
10. Chancollon . Odile . Pusineri . Claire . Ridoux . Vincent . Food and feeding ecology of Northeast Atlantic swordfish (Xiphias gladius) off the Bay of Biscay . ICES Journal of Marine Science . 1 September 2006 . 10.1016/j.icesjms.2006.03.013 . 63 . 6 . 1075–1085. free .