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I have a question about the channel and ligula in young male octopuses and why males are not identifiable from birth. I could see where the ligula might grow with maturity but how would the channel not be there from birth?
It probably is D (I stress the PROBABLY bit), but you'd need a microscope to see it. Not really what you want to subject a young octopus to.
I can sex most things, when they're preserved (i.e., not moving). It can prove challenging for squid, even as submature, but octopus are generally much easier. I also use a scalpel ..... so I'll shut up at this point (these are preserved museum specimens).
Thanks for confirming I am at least thinking clearly. I have been reading write-up on the hummelincki (written in the 1950's) and they could not tell from the preserved juveniles so it made me curious as to why this one feature would not be always present.
It would be, but it would be very small. There are a few knobs and papillae on the surface of the visceral mass of a juvenile that could easily be mistaken for a (cough) boy bit in a juvenile, and sometimes differentiating these from female genital structures is difficult in a juvenile. But it can be done with a lot of experience, and an ontogenetic series of specimens to help identify where the structures will be at any given size.
I've been dissecting out the intestinal and ink sac arteries of a small subadult species of Pareledone today; it just takes time, non-shakey hands, great care, and a microscope. I was showing someone, and am pleased that I didn't make a dog's breakfast if it because it has been 13 years since I last did this.
Why? Well, many species that lack a functional (and visible) ink sac retain the ink-sac artery. It is such a conservative character - the ink-sac arterial origin in Eledone is exactly the same as in Paraledone - northern and southern hemisphere taxa. We're tracking it in other octopus taxa for a Masters thesis here (which makes me think we should look also at a squid ... just to see how conservative it actually is!). I love this site - you get to think out loud.
But in the octopus, wouldn't the arm show something of the spermatphore channel? I can understand not seeing it in teeny tiny ones but the mantle size on the juveniles they could not determine was large enough that the arms should have been well developed. They were looking for boy and girl parts but the third right arm is known to be the hectocotylus in this species and it would seem the channel would be visable under a microscope very early.
It would be curious to see if the ink sac could be made functional by pressing some of the gene buttons. I am thinking of the article Kat brought up awhile back where they were experiment with a gene that allowed regeneration of body parts in chickens while still in the egg.
I have always found the spermatophoral groove to be far more obvious than any terminal modification of the arm (calamus, lugula, jointly = hectocotylus), so I would have thought that this structure would have been relatively well developed even in a juvenile. (I wouldn't say it was apparent in a paralarval, pelagic form though, but in the benthic forms probably some structure was apparent, if only at a microscopic level.)
I went back and verified the study and the 21 unsexed hummelincki octos had mantle lengths form 6-9.5 mm so they were benthic at the time of capture (the study was published in 1966). It is necessary to confirm sex with organs when other identifying traits are known?
I am always more comfortable with confirmation of sex by more than one character. 10 mm is actually quite large, so I would have thought that sexing wasn't that difficult at all (I've done this one specimens before).
Some of the best research on cephalopods was conducted around 1900-1930, so I wouldn't worry to much about the age of the publication. The research done with whale-oil lamps and crappy old microscopes (relative to what equipment we have today) leaves a lot of the modern stuff for dead!