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One octopus detaches an arm and sends it swimming

It swam off so convincingly that science named it as a parasite.

One octopus detaches an arm and sends it swimming
Photo: James St. John · CC BY 2.0 · Wikimedia Commons

The male argonaut is a fraction of the female's size. He fills a specialised arm, the hectocotylus, with sperm, detaches it, and it swims away under its own power to find her and deposit its contents. He does not go with it.

When 19th-century naturalists found these arms inside female argonauts, they assumed they were parasitic worms and gave them a genus name — Hectocotylus. Georges Cuvier named it in 1829. It took until the 1850s for anyone to work out that the worm was a male octopus's arm.

Sources

Cuvier (1829); Norman et al., Proceedings of the Royal Society B (2002)

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