Seven-arm octopus
species of mollusc
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). 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.
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.
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.
Older specimens have been found to have shorter bodies and longer arms than juveniles.
While juveniles tend to be translucent, one study in 1985 in Norway studied the morphology between two female H. Atlanticus specimens, with one being a dark purple and the other a pale blue/white.
This brief starts where responsible research should: with the source description of “Seven-arm octopus” as species of mollusc. Everything that follows is an evidence route, not borrowed authority.
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The subject matters to the science & nature register because the source frames it as species of mollusc. Its deeper value depends on whether names, dates, institutions and citations support that framing.
Datasets, specimens, observations and peer-reviewed methods provide the appropriate test for the technical claims summarized here. The source revision retrieved here is dated Aug 31, 2026. The linked authority identifier is Q603484. None of the 0 selected statements returned an explicit reference. The first chronological checks are 1922, 1880, 1929 and 1985.
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This entry incorporates text from “Seven-arm octopus” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.