Anatomy question

[George Sims]

Dr. Birk,
Thanks for taking time to reply. I can visualize the structure much better. It must be exceptionally flexible and compressible.
How large is the brain compared to the beak? I understand that octopuses can squeeze through openings just large enough to accommodate the beak. If the brain were larger, it would have to be compressed, which does not seem to be a very beneficial process for the animal.

 

[DWhatley]

@CephBirk I have only kept one bimac but I also noticed that there is a similar (and possibly shape limiting) cartilage like thickness in O. hummelincki. O. briareus and O. mercatoris definitely do NOT have it and I don't recall noticing it on the one vulgaris. I often wondered if O. hummelincki was somewhat restricted in what it could squeeze through because of the density of the area.

 

[CephBirk]

How large is the brain compared to the beak? I understand that octopuses can squeeze through openings just large enough to accommodate the beak. If the brain were larger, it would have to be compressed, which does not seem to be a very beneficial process for the animal.

I suppose it depends on how you define the "brain". The width of the beak is pretty similar in size to the "core" of the brain (that being the supra- and suboesophageal lobes), but if you include the optic lobes, which are bigger than the rest of the brain combined, then the brain is quite a bit larger than the beak. It does make me wonder where this oft repeated idea of the beak being the size limiter comes from...

 

[TheSeeker]

I suppose it depends on how you define the "brain". The width of the beak is pretty similar in size to the "core" of the brain (that being the supra- and suboesophageal lobes), but if you include the optic lobes, which are bigger than the rest of the brain combined, then the brain is quite a bit larger than the beak. It does make me wonder where this oft repeated idea of the beak being the size limiter comes from...

There are so many chliches about the octopus such as this one. I was discussing this with a friend and we came to the conlcusion that probably when octopuses were first introduced to public aquaria, in order to increase the public's interest about them, a lot of stories and myths were invented and are being reproduced up to today...

 

[George Sims]

There are so many chliches about the octopus such as this one. I was discussing this with a friend and we came to the conlcusion that probably when octopuses were first introduced to public aquaria, in order to increase the public's interest about them, a lot of stories and myths were invented and are being reproduced up to today...

This is good to know. I thought the story about the beak was gospel. Thanks.

 

[DWhatley]

This is good to know. I thought the story about the beak was gospel. Thanks.

No such thing in science and particularly with octopuses. Everytime we see a generalization, we ultimately find an exception. In the last few years it was that ALL octopuses lay eggs only once and then die. We now know of at least 2 species that lay multiple clutches. The first time this was discovered, the person making the discovery was not believed and ultimately turned away from science and made his living as an artist.

 

[George Sims]

No such thing in science and particularly with octopuses. Everytime we see a generalization, we ultimately find an exception. In the last few years it was that ALL octopuses lay eggs only once and then die. We now know of at least 2 species that lay multiple clutches. The first time this was discovered, the person making the discovery was not believed and ultimately turned away from science and made his living as an artist.

Would that be Arcadio Rodaniche? I’m finishing up Godfrey-Smith’s book.

 

[DWhatley]

Would that be Arcadio Rodaniche? I’m finishing up Godfrey-Smith’s book.

Yes! Another "known physiological fact" we have debunked is that octopuses can't hear. Then there is the mystery of color blind animals being able to approximate the colors of their surroundings (this one still does not have a definitive answer and the current guesses are a bit weak)

 

[TheSeeker]

It's is very difficult to make definite statements about octopuses. Not only there are many different species, each with its own behavior and characteristics, but even within the same species you can encounter extremely striking variations, if not in the physiology then definitely in the behavior of each individual. Even the tales of fishermen illustrate this fact: every fisherman remembers of a particular octopus which has done something out of the ordinary...Yes, fishermen are known for their tall tales, but there is truth hidden in every story.

 

[George Sims]

Are all the other organs rather loosely contained within a fluid-filled mantle, then, or are they confined within muscular “compartments”?

It looks like Hanlon & Messenger have answered my questions about the mantle. Great book! On p. 12:
“The mantle is so organized around the viscera that it forms a sheltered space, the mantle cavity, in which the gills lie and into which the gut, ‘kidneys’ and gonads open. In cephalopods this mantle cavity constitutes a system for locomotion (‘jetting’) as well as for respiration. The viscera include elaborate circulatory, excretory, digestive and reproductive systems.”
I’ve read four or five popular ceph books in the last month, preparing me for this book, which is full of cool details.