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Joe-Ceph;178997 said:In theory sure, but I'll bet you haven't tried to sex a bimac.
I think you can only count the arms if looking at the top or the bottom (sucker side) of the octopus, I'm not sure what "facing you" means.
I've only sexed O. Hummelincki, O. Briareus, O. Rubescens, and E. Dofleini. What I mean by facing you is imagine the animal sitting on a table with it's mantle flopped over away from you with it's eyes looking directly at you and arms L1 and R1 pointing at you. That's what I mean by facing you.
I think a more clear way to describe it would be:
Imagine that the octopus is stuck to the wall, with its eyes looking up at the ceiling, and it's "head bag" hanging down toward the floor (you are looking at the "top" of the octopus). The two arms pointing up are called L1 and R1 (Left-1, Right-1). R1 is at 1 O'clock, L1 is at 11 O'clock. Count clockwise from R1, to find R2, R3, and R4. Count counter-clockwise from L1 to find L2, L3, and L4. The hectocotylus is at the end of R3.
You're right, you did a much better job at explaining it.
Bimacs are particularly hard to sex because the hectocotylus is very small (2% of arm length) and only developed in adults, so sexing a small one is impossible (so I've read). Add to that the fact that the bimac is squirming and slippery. In a tank, at home, I had to take lots of pictures of my bimac before I was able to find one showing the tip of R3 that I could blow up. In the field I've found it close to impossible short of snipping off the end of R3 and studying it (which I haven't done). I've read that females say "excuse me" after they ink, while males just snicker, but I haven't observed that myself.
I've sexed my E. Dofleinis but that was in a 1000 gallon system of course. I pulled it to the surface and wrestled it's arm from the others to sex it. It wasn't too difficult, but their hectocotylus is very prodominant.