Seven-arm octopus

Seven-arm octopus
File:Haliphron atlanticus (70 mm ML).jpg
Ventral view of young female (70 mm ML)
File:Haliphron atlanticus1.jpg
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 (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). 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

File:Haliphron atlanticus embryos.jpg

Egg string and embryos of H. atlanticus collected north of the Cape Verde Islands (). 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 . It is deposited at the Zoologisk Museum, University of Copenhagen.

In 2002, a single specimen of giant proportions was caught by fishermen trawling off the eastern Chatham Rise, New Zealand. This specimen, the largest of this species and of all octopi, 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.

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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

• 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.

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