Sexing an Octopus - Photos of Hectocotylized Arm

DWhatley

Cthulhu
Staff member
Moderator
#1
One of the first questions a new octopus keeper asks is for help identifying the sex of their new ward. Usually the easiest way to sex an octopus is by observing the third arm to the right (clockwise) on a sexually mature animal. This arm (hectocotylus) has a suckerless tip (ligula) and a channel for delivering spermataphores. The ligula is very difficult to identify while looking at a live animal but can be just be seen in the second (hummelincki) photograph. The channel is easier to see in photographs than trying to view it on a moving animal and is seen as a white line in the third (briareus) photograph. The easiest way to identifiy it is to see if the octopus keeps it rolled up protectively (all photos). SueNami (the briareus in photos 1 and 3) came with this arm removed up to the webbing. The assumption was that a male would be less likely to loose the arm and we assumed female. As the arm regrew we discovered that we have a boy named Sue and that the hectocotylized arm appears to grow back normally (functionality can only be assumed).

Video from @sedna that shows O. briareus hectocotylus
 

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DWhatley

Cthulhu
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Moderator
#6
The specialized arm is common to most male octopuses (I recently read a paper that said one species drops a normal arm and grows out hectocotylized arm when it is sexually mature) but not every species roles up the arm. The arm is used (by some more than others) as an arm too but you will usually see it curled when not in direct use. My unknown species Macropus male only curls the tip (and then it is more just at right angles to the arm rather than curled) and it took me three month to see the specialized end (the ligula will not have suckers). Puddles moves his arms around a lot and is nocturnal so the limited lighting has made him difficult to sex.
 

DWhatley

Cthulhu
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Moderator
#9
:smile:Certainly biologically interesting. It is not seen by the observer as it appears to happen only when they are depositing the spermataphores while the ligula is inside the mantle. The scientist first noticed the physical change during a failed mating attempt.
 

mucktopus

Haliphron Atlanticus
Staff member
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#10
neurobadger;154317 said:
Good crud, octopuses get erections too? (That appears to be what the latter article says.)
We have evidence for this in the wild too (Amphioctopus marginatus)- we hope the short little note, with frames of video, will be out this summer.
 

DWhatley

Cthulhu
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Moderator
#11
We have evidence for this in the wild too (Amphioctopus marginatus)- we hope the short little note, with frames of video, will be out this summer.
I thought about asking you if you had seen this (I just ran across the paper while looking for an external reference for ligula) since you have seen more in situ matings than the rest of us combined (including Roy or we have almost no numbers at all :sagrin:) .
 

CaptFish

Colossal Squid
Staff member
Moderator
#16
Bump...


On the third arm, hectocotylus, how much of the tip will be suckerless, ligula, say on a Hummelincki or Vulgaris?

At what age does an octopus become sexually mature? is it the same age for male and female?
 

DWhatley

Cthulhu
Staff member
Moderator
#17
I put a list of papers I found on hummelicki in the Cephalopod Species (by family)->Octopodidae forum. The first paper has this to say about ligula length:
Hectocotylus
on right third arm, ligula small, LLI about 3.0-5.0, calamus spout usually midwayan ligula.
. It is my guess that the calamus spout would be the part of the ligula that would be suckerless :bonk:

With the eye spots, Penney will not be vulgaris but someone else may know of a reference with similar info on vulgaris.
 

CaptFish

Colossal Squid
Staff member
Moderator
#18
Hmmm I thought the whole suckerless part was ligula and the calamus spout is where spermataphores come from...


She's a Vulgarlicki! Too big to hummelincki, and possible eye spot equals not Vulgaris. I wish someone knew!
 

Steve O'Shea

Colossal Squid
Supporter
#19
I've never heard of a 'calamus spout' - the calamus and ligula are quite different structures, neither with suckers. I think someone has been making up words. Bizarre.
 

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