Welcome to TONMO, the premier cephalopod interest community. Founded in 2000, we have built a large community of experts, hobbyists and enthusiasts, some of whom come together when we host our biennial conference. To join in on the fun, sign up - it's free! You can also become a Supporter for just $50/year to remove all ads and enjoy other perks, like Site Search. Follow us on Twitter or Facebook for more cephy goodness.
Roy Caldwell Photos Wunderpus Hectocotylus Roy Caldwell (Neogonodactylus) provided permission to post a prerelease copy of these photos. First photo: The third right arm is clearly visiable. This male is small, but was capable of producing and transferring spermatophores. Second photo: The hectocotylus tip showing the ligula and spermatophoral groove. Third photo: The tip of the hectocotylus is usually coiled, but you can see where the ligula folds back on itself.
The ligula of aculeatus can be as small as 1.5 mm, so really hard to see. Look instead for the groove along the back edge of this arm, which will appear tube-like in big males with enlarged suckers (not your octo) but a thin white line in juveniles. Basically, if the back edges of all arms look the same then it's a female.
The attached pic shows a male hopping on it's hectocotylus- you can vaguely see the groove along the inner edge of the arm. Hope this helps!
(wait- turns out my bandwidth isn't cutting it- Tony if I email you the pic can you please post it?)
LOL, You and Roy insist that the channel is easy to see but I can never find it without a photo. I think it is because they never hold their arms still while I am trying to watch . I don't know how you see details in situ!
Sexing an Octopus - Photos of Hectocotylized Arm It isn't always easy to sex an octopus, but it is fairly simple to tell if an Abdopus aculeatus is male. When the animal climbs onto the front wall of the aquarium (which they usually will do), look at the suckers near the base of the first and second pair or arms. In mature males, they are enlarged. They are smaller in females and juveniles. The hectocotylized arm of the male is also easy to spot. It is the third, right arm. In this shot it looks like the fourth, but it's actually the third. When they look to the side they usually stick their eye over the web between arms I and II- so the left arm I is draped over to the right side, throwing off the count. Note the spermatophoral groove on the trailing edge. It extends the entire length of the arm. Not visible is the small ligula on the tip of the arm.