Homeosis or atavism?

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.

Ugh, still getting the "newbiadguide.com" redirection spam.

I think all octopi have 9 tentacles, but they move around so much that no cephologist has ever managed to count 'em.

Yep! The proof is this one wasn't noticed until after it had been boiled. They aren't moving then.

So, in the old days, an ancestor of a modern octopus would be called a "decopus"?

Looks like one tentacle bifurcated. Sometimes happens with fingers or metacarpals.

"Looks like one tentacle bifurcated. Sometimes happens with fingers or metacarpals."

But of course, unlike phalanges, but like bananas, tentacles have no bones.

the primitive condition in cephalopods is to form ten arms;

Well, 10 or 20?

(Thanks for the link. I seem to have missed a lot in July.)

But of course, unlike phalanges, but like bananas, tentacles have no bones.

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.

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!!!

Homeosis or atavism? Neither. I'm going with meristic phenocopy. But I could be wrong.

A nine-tentacled octopus is a contradiction in terms. Clearly what you've got here is an enneopus.

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…

A female with the two tentacles bifurcated was found within a sample of 54 specimens of Moroteuthis
ingens collected by a Spanish trawler fishing in the SouthAtlantic around the Falklands Islands dur-
ing the austral spring of 2004.This is the first case of double tentacle bifurcation reported for this
oegopsid squid and also for cephalopods.In spite of the lack of normal tentacles,the specimen does
not show signs of malnutrition.Potential causes for this anomaly,implications to the feeding behav-
iour of the animal and the regeneration process are discussed.

A Softer World

This seemed appropriate.

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.

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!

"Yes, but bone isn't needed."

For tentacles? Or bananas?

(Here is the tune with seasonally appropriate visuals! AND a baby!)

Photoshop.

from the article:

"In Akashi, we might see one every 20 years or so. They are extremely rare."

Koita says he will show off the octopus for a few days before selling it to a lucky customer.

One in 20 years, and the decision is to sell it to a "lucky customer" instead of preserving it for further study.

*sigh*

May be a meristic variation possibly caused by some environmental stressor. Ideal for a tentaculo de pulpo a la cacerola gallega for nine persons.

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.

"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.

Looks like one tentacle bifurcated. Sometimes happens with fingers or metacarpals.

the primitive condition in cephalopods is to form ten arms;

Well, 10 or 20?

(Thanks for the link. I seem to have missed a lot in July.)

But of course, unlike phalanges, but like bananas, tentacles have no bones.

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.