How do you tell a boy octopus from a girl octopus?

Lindsay McGuire

Larval Mass
My son, John, age 9, is doing a research project on the octopus :grad:, and is having a difficult time coming up with a comprehensible description of how to tell a boy from a girl. Can anyone help him out?
With profound thanks from Maine,
John's mother

Steve O'Shea

Colossal Squid
Hi John's mum (?Lindsay is it). How much time have you got? If the project can wait two days then I can get back in to work and respond with a couple of photographs of boy/girl characters. Basically the tip of the third right arm (or, rarely third left) of the male octopus is modified into a scoop/shovel (calamus/ligula) - there are no suckers at the end (the female has all 8 arms attenuating to fine, sucker-bearing tips.

There is a section online already that might help ('A guide to frequently used characters, states and measures') that has illustrations of this scoop/shovel (hectocotylus). Please see Figure 4 at

I'll post additional pics of whole animals in 2 days

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