An octopus with only seven arms: Anatomical details

Ian G. Gleadall

Research output: Contribution to journalArticlepeer-review

8 Citations (Scopus)


A male specimen of Octopus is described which has only seven arms: the fourth right arm is congenitally absent. Dissection reveals that, as in normal octopuses, eight brachial nerves arise from the brain. However, right brachial nerves 2, 3 and 4 are connected by unusually short lengths of the interbrachial commissure, distal to which right brachial nerves 3 and 4 run together, with corresponding arteries, into the third right arm. Hectocotylization of the latter confirms that it is the fourth right arm which is missing. Other abnormalities of the specimen include an obviously asymmetrical funnel organ and three pairs of conjoined suckers.An old specimen of Octopus described as having only seven arms was re-examined for comparison. This animal, too, appeared to have no fourth right arm, but on closer inspection the extremely short stump of this arm was discovered.

Original languageEnglish
Pages (from-to)479-487
Number of pages9
JournalJournal of Molluscan Studies
Issue number4
Publication statusPublished - 1989 Nov 1

ASJC Scopus subject areas

  • Aquatic Science
  • Animal Science and Zoology


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