Sexing an Octopus - Photos of Hectocotylized Arm

Damage to an arm might account for the missing suckers. One of my hummelincki's has an arm that was partially removed in situ and a portion of it grew back with no suckers.
 
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.
 

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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?)
 
Crissy,
LOL, You and Roy insist that the channel is easy to see but I can never find it :biggrin2: without a photo. I think it is because they never hold their arms still while I am trying to watch :roll:. 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.
 

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A. aculeatus ligula Like Mucktopus said, the ligula in this species is small. This is the best photo I have of it. It is the claw-shaped object at the center of the whirl. Roy
 

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Better shots of A. aculeatus ligula The last shot that I posted of the ligual was not very clear since males usually keep the tip of the hectocotylus coiled. These shots are slightly better. Roy
 

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Sexing an Octopus - Photos of Hectocotylized Arm I know I've posted photos of a blue-ring's hectocotylus before, but this animal is an undescribed species three times the size of any other blue-ring. (I also wanted to show off my new Nikon D800. Roy
 

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Sexing an Octopus - Photos of Hectocotylized Arm Male octopus usually keep their hectocotylus tucked in tight away from possible damage. For this reason it is difficult to photograph the hectocotylus tip which bares the ligula. I got a chance to photograph this male's ligula this morning. Roy
 

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I have read in several sources (though I did not document them) that E. dofleini is one of the primary octopus species MOST characterised by sexual dimorphism by sucker size on at least two arms. (Males possessing the enlarged suckers.)

I’m sorry I don’t have a citation, but I swear I just read this assertion again—three times in a week or five days—just last week. So... the idea’s out there, and it didn’t come off of some wanker’s Tumblr blog—the sources were quite legitimate. Enough to warrant a raised eyebrow, at least.

Cheers and good luck...
 

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