…and this is a 
Homeosis or atavism?
Category: Cephalopods • Organisms
Posted on: October 28, 2007 11:41 AM, by PZ Myers
This is pretty nifty: it's a nine-tentacled octopus. Count 'em!
If I may be so bold as to remind you all of the basics of cephalopod development and evolution, the primitive condition in cephalopods is to form ten arms; in the octopods, one pair is secondarily lost by some unidentified suppression in development. It's not too surprising that there would be some low frequency of re-expression of members of the fifth and normally missing pair — and the article mentions that the Akashi Seafood Council reports that they see this once in every 20 years or so.
They should keep an eye open for these kinds of developmental abnormalities — they can be an indicator of stressors in the environment if the frequency starts to rise.
Comments
I think all octopi have 9 tentacles, but they move around so much that no cephologist has ever managed to count 'em. Eight is just a theory you know.
Posted by: Scrofulum | October 28, 2007 11:45 AM
Ugh, still getting the "newbiadguide.com" redirection spam.
Posted by: Hank | October 28, 2007 12:08 PM
Yep! The proof is this one wasn't noticed until after it had been boiled. They aren't moving then.
Posted by: blf | October 28, 2007 12:09 PM
So, in the old days, an ancestor of a modern octopus would be called a "decopus"?
Posted by: greg laden | October 28, 2007 12:28 PM
Looks like one tentacle bifurcated. Sometimes happens with fingers or metacarpals.
Posted by: David Marjanović, OM | October 28, 2007 12:35 PM
"Looks like one tentacle bifurcated. Sometimes happens with fingers or metacarpals."
But of course, unlike phalanges, but like bananas, tentacles have no bones.
Posted by: Sven DiMilo | October 28, 2007 12:41 PM
Well, 10 or 20?
(Thanks for the link. I seem to have missed a lot in July.)
Yes, but bone isn't needed. When such a bifurcation happens, it happens before even the cartilage forms that is later replaced by bone. Whenever you have an axis in development, you can mess with it so it bifurcates, I think.
Posted by: David Marjanović, OM | October 28, 2007 1:17 PM
I'm no developmental biologist, but it seems odd to me that if another tentacle were to be produced due to expression of ancestral states, but the tentacles are produced in pairs... shouldn't there be two more tentacles.
Tell me more!!!
Posted by: Nutmeg | October 28, 2007 1:34 PM
Homeosis or atavism? Neither. I'm going with meristic phenocopy. But I could be wrong.
Posted by: Colugo | October 28, 2007 1:38 PM
A nine-tentacled octopus is a contradiction in terms. Clearly what you've got here is an enneopus.
Posted by: K. Signal Eingang | October 28, 2007 3:02 PM
I agree with David; if you look at the morphology of all 9 arms, you notice quickly that there are two next to each other that are slightly narrower, with smaller suckers, than the rest.
also, note that one of the two slightly smaller arms has its sucker lines terminating at the connection with its neighbor arm, not proceeding to the mouth area like the rest do.
It indeed does look like an issue of bifurcation of one of the arms, rather than an independent arm.
octopus can easily regenerate a damaged arm, and it might have produced a bifurcation, if this isn't a case of a developmental defect.
from the lit:
http://72.14.253.104/search?q=cache:Z_RG0vKnXQAJ:www.mba.ac.uk/jmba/pdf/5529.pdf+octopus+regenerate+bifurcated&hl=en&ct=clnk&cd=1&gl=us
Posted by: Ichthyic | October 28, 2007 6:24 PM
A Softer World
This seemed appropriate.
Posted by: Spike | October 28, 2007 6:38 PM
Last night the Divine Ms. Gina and I were walking to a restaurant about a mile away. As we passed under a railroad underpass, I noticed that someone had plastered a big sticker of an octopus on it. Being a geek, I counted the arms. It was a nonapod.
Wish I remembered the URL on the sticker.
Posted by: cory | October 28, 2007 6:39 PM
This octopus is just trying to "fill the gaps" between 8 and 10, you know? Of course, he just created two new gaps-- 8.5 and 9.5!
Posted by: DaveX | October 28, 2007 8:11 PM
"Yes, but bone isn't needed."
For tentacles? Or bananas?
(Here is the tune with seasonally appropriate visuals! AND a baby!)
Posted by: Sven DiMilo | October 28, 2007 9:17 PM
Photoshop.
Posted by: Bert Chadick | October 28, 2007 9:54 PM
from the article:
One in 20 years, and the decision is to sell it to a "lucky customer" instead of preserving it for further study.
*sigh*
Posted by: Ichthyic | October 28, 2007 11:55 PM
May be a meristic variation possibly caused by some environmental stressor. Ideal for a tentaculo de pulpo a la cacerola gallega for nine persons.
Posted by: jaim klein | October 29, 2007 12:14 PM
I may have sprained my banana bone, but (as some have noticed) one arm is a little smaller and appears to be a bifurcation of the arm near it... and would this sort of thing more likely indicate a regeneration gone awry (given that cephalopods regenerate somewhat easily), perhaps during development even, rather than jumping to the elaborate genetic explanation (I'm being repressed!) Just a thought. As I say, my banana bone is out of wack, and I'm trying to preserve my bodily fluids.
Posted by: OweinH | October 31, 2007 12:43 AM
"Homeosis or atavism? Neither."
I agree. Physical or chemical disruption leading to a bifurcation seems most plausible.
First post from a North American time zone! I feel on the Pharyngula cutting edge.
Posted by: miko | November 1, 2007 6:01 PM