Seven-arm octopus

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

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 3.5 m (11 ft) and mass of 75 kg (165 lb).[3][4] 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.[2]

Below includes a description of the octopus' traits, distribution patterns, reproduction, and ecology.

Traits

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.[5]

Unlike most octopods, H. atlanticus has a swim bladder, an organ evolved from its digestive system. The swim bladder allows it to maintain neutral buoyancy, neither sinking nor rising in the water column.[6]

Older specimens have been found to have shorter bodies and longer arms than juveniles.[7]

While juveniles tend to be translucent, one study in 1985 in Norway studied the morphology between 2 female H. Atlanticus specimens, with one being a dark purple and the other was a pale blue/white.[7] Video evidence from the Monterey Bay Aquarium Research Institution (MBARI) was released showing a red specimen as well[8], giving the species a color range of blue to red when adults.

Distribution

H. atlanticus is found worldwide in tropical and temperate waters.[9]

The type specimen was collected in the Atlantic Ocean at 38°N 34°W / 38°N 34°W / 38; -34 (west of the Azores). It is deposited at the University of Copenhagen Zoological Museum.[10]

Since then, several specimens have been caught throughout the Atlantic, as far as the Azores archipelago[11] and near South Georgia Island.[12]

In 2002, a single specimen of giant proportions was caught by fishermen trawling at a depth of 920 m (3,020 ft) 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 0.69 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.[3][4]

Another specimen was reported from Skjørafjorden, Norway, where a female was captured in a trawl net at approximately 100 m (328 ft) depth in November 2000. The individual measured about 96 cm (3.1 ft) in total length, though the arm tips were damaged, and weighed 8.5 kg (18.7 lb) when received by researchers. The specimen had a soft, gelatinous body with a reddish coloration and rows of pale suckers, and was later preserved and deposited at the NTNU Museum of Natural History and Archaeology in Trondheim.[13]

Evidence of the species in northern waters is also supported by dietary studies of sperm whales, which have contained remains of H. atlanticus in their stomach contents. Because these whales are believed to feed in Arctic and northern boreal waters before migrating south, these findings suggest that the species likely occurs more widely in the Norwegian Sea and nearby Arctic regions than the relatively small number of direct captures of indicate.[13]

There have also been multiple sightings of H. atlanticus in Monterey Bay in the Northeast Pacific Ocean.[14]

Mating and reproduction

The mating of H. atlanticus is poorly researched, but it is predicted to occur sporadically on the continental coast.[15]

Dwarf males of H. atlanticus have been discovered. These males have invested energy for growth into reproductive traits such as a spermatophore and a muscular penis. They also possess a detachable hectocotylus which is used to transfer the spermatophore into their mates. These males qualify as dwarf males as they are only 5-15% of the size of a maximum female specimen of H. atlanticus.[6] The organism's swim bladder helps them maintain buoyancy in the deep sea without expending large amounts of energy searching for mates.[6]

Ecology

Isotopic,[12] photographic and video evidence[11] have shown complex interactions between H. atlanticus and jellyfish and other gelatinous zooplankton, from feeding to protection, respectively. H. atlanticus specimen have been observed feeding in mesopelagic areas, particularly at the ridges of seamounts.[15] Stable isotope analyses indicate that H. atlanticus occupies an intermediate trophic level among deep-sea cephalopods, consistent with feeding on gelatinous zooplankton as well as other prey types.[16]

Predators of H. atlanticus include the blue shark, sperm whale, Hawaiian monk seals, and swordfish.[15][17][18][19][20][21] This may be in part due to the diel vertical migration and deep-diving abilities of some of these species. On rare occasion, lancetfish and some species of tuna will predate on H. atlanticus. H. atlanticus has been found in the stomach contents of shorebirds like Cory's shearwater, which predate on the octopus after it is driven to the surface by tuna and marine mammals.[22]

Potential divergence of species

Though widely considered monospecific, there is genetic evidence that there are multiple Haliphron species, with at least one in the South Pacific and one in the North Pacific.[23]

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. ^ Allcock, L. (2014). "Haliphron atlanticus". IUCN Red List of Threatened Species. 2014 e.T163207A983527. doi:10.2305/IUCN.UK.2014-3.RLTS.T163207A983527.en. Retrieved 19 November 2021.
  2. ^ a b Julian Finn (2017). "Haliphron Steenstrup, 1859". World Register of Marine Species. Flanders Marine Institute. Retrieved 5 February 2018.
  3. ^ a b O'Shea, S. (2002). "Haliphron atlanticus — a giant gelatinous octopus" (PDF). Biodiversity Update. 5: 1.
  4. ^ a b O'Shea, S. (2004). "The giant octopus Haliphron atlanticus (Mollusca: Octopoda) in New Zealand waters". New Zealand Journal of Zoology. 31 (1): 7–13. Bibcode:2004NZJZ...31....7O. doi:10.1080/03014223.2004.9518353. S2CID 84954869.
  5. ^ "About Live Science". livescience.com. 2023-03-02. Retrieved 2025-01-20.
  6. ^ a b c Roura, Alvaro; Bañón, Rafael; de Carlos, Alejandro; Valeiras, Julio; Abad, Esther; Serrano, Alberto; Guerra, Angel (2024-06-27). "Dwarf males of the seven-arm octopus, Haliphron atlanticus: morphology and adaptations". Journal of Molluscan Studies. 90 (3) eyae025. doi:10.1093/mollus/eyae025. ISSN 0260-1230.
  7. ^ a b Willassen, Endre (10 Aug 1985). "Haliphron Atlanticus Steenstrup (Cephalopoda, Octopoda) from the coast of Norway". Sarsia. 71 (1): 35–40 – via TandF.
  8. ^ Mackenzie, RJ. (18 December 2025). "Rare Footage Reveals the Mysterious Seven-Arm Octopus Eating Its Prey". Discover Magazine.
  9. ^ "Seven-arm octopus". Monterey Bay Aquarium Research Institute.
  10. ^ "Current Classification of Recent Cephalopoda" (PDF). Archived from the original (PDF) on 2006-01-01. Retrieved 2007-01-14.
  11. ^ a b 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. 49: 495–499. doi:10.1007/s12526-017-0767-3. S2CID 255616524.
  12. ^ a b 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. Bibcode:2015MEPS..530..119G. doi:10.3354/meps11266.
  13. ^ a b Bakken, Torkild; Holthe, Torleif (2002-12-31). "Haliphron atlanticum (Cephalopoda, Alloposidae) caught in Skjørafjorden (64°N), Norway". Fauna norvegica. 22: 37–38. doi:10.5324/fn.v22i0.5988. ISSN 1891-5396.
  14. ^ Mauhay-Moore, Sam (Dec 11, 2025). "Giant, rare 7-armed sea creature spotted in California's Monterey Bay". SFGate.com.
  15. ^ a b c Miller, Michael J.; Miwa, Tetsuya; Watanabe, Shun; Kuroki, Mari; Higuchi, Takatoshi; Takeuchi, Aya; Serizawa, Kenta; Okino, Tatsufumi; Tsukamoto, Katsumi (2018). "Observation of a Gelatinous Octopod, Haliphron atlanticus , along the Southern West Mariana Ridge: A Unique Cephalopod of Continental Slope and Mesopelagic Communities". Journal of Marine Biology. 2018: 1–11. doi:10.1155/2018/6318652. ISSN 1687-9481.
  16. ^ Miller, Michael J.; Miwa, Tetsuya; Watanabe, Shun; Kuroki, Mari; Higuchi, Takatoshi; Takeuchi, Aya; Serizawa, Kenta; Okino, Tatsufumi; Tsukamoto, Katsumi (2018). "Observation of a Gelatinous Octopod, Haliphron atlanticus , along the Southern West Mariana Ridge: A Unique Cephalopod of Continental Slope and Mesopelagic Communities". Journal of Marine Biology. 2018: 1–11. doi:10.1155/2018/6318652. ISSN 1687-9481.
  17. ^ Henderson, A. C.; Flannery, K.; Dunne, J. (May 2001). "Observations on the biology and ecology of the blue shark in the North-east Atlantic". Journal of Fish Biology. 58 (5): 1347–1358. Bibcode:2001JFBio..58.1347H. doi:10.1111/j.1095-8649.2001.tb02291.x.
  18. ^ Goodman-Lowe, G. D. (29 October 1998). "Diet of the Hawaiian monk seal (Monachus schauinslandi) from the Northwestern Hawaiian islands during 1991 to 1994". Marine Biology. 132 (3): 535–546. Bibcode:1998MarBi.132..535G. doi:10.1007/s002270050419. S2CID 84310964.
  19. ^ Chua, Marcus A.H.; Lane, David J.W.; Ooi, Seng Keat; Tay, Serene H.X.; Kubodera, Tsunemi (5 April 2019). "Diet and mitochondrial DNA haplotype of a sperm whale (Physeter macrocephalus) found dead off Jurong Island, Singapore". PeerJ. 7 e6705. doi:10.7717/peerj.6705. PMC 6452849. PMID 30984481.
  20. ^ Clarke, M.R.; Pascoe, P.L. (11 May 2009). "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. 77 (4): 1255. doi:10.1017/S0025315400038819. S2CID 86637228.
  21. ^ Chancollon, Odile; Pusineri, Claire; Ridoux, Vincent (1 September 2006). "Food and feeding ecology of Northeast Atlantic swordfish ( Xiphias gladius ) off the Bay of Biscay". ICES Journal of Marine Science. 63 (6): 1075–1085. Bibcode:2006ICJMS..63.1075C. doi:10.1016/j.icesjms.2006.03.013.
  22. ^ Granadeiro, Jp; Monteiro, Lr; Furness, Rw (1998). "Diet and feeding ecology of Cory's shearwater Calonectris diomedea in the Azores, north-east Atlantic". Marine Ecology Progress Series. 166: 267–276. doi:10.3354/meps166267. ISSN 0171-8630.
  23. ^ Lima, Françoise D.; Mendes, Liana F.; Veras, Leonardo; Leite, Tatiana S.; Lima, Sergio M. Q. (2017-01-13). "The Seven-arm Octopus, Haliphron atlanticus Streenstrup, 1861 (Cephalopoda, Alloposidae), in the Fernando de Noronha archipelago, Brazil". Check List. 13 (1): 1–5. doi:10.15560/13.1.2036. ISSN 1809-127X.

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. doi:10.1080/00364827.1986.10419671.
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