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left-right asymmetry in cephalopods

monty

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#1
I just heard a talk that discussed the molecular control of the development of left-vs-right differences in gastropods that was interesting. I think it's unpublished work, so I'm not going to mention details, but I think it's safe to say that the mechanism for determining left-handed or right-handed spirals in snail shells is controlled by a mechanism more like the one in vertebrates than like the one in arthropods, which is interesting.

Naturally, I was interested in how this may apply to cephalopods. Modern shelled cephs seem to have bilaterally symmetric shells, but certainly some ammonoids are "dextral" (clockwise when looking down at the point) or "sinistral" (the other way), and I'm not sure about nautiloids. All(?) modern cephs have sexual dimorphism in a left-or-right sense, except maybe the squids that have an internal penis instead of a hectocotylus. I can't remember if there are asymmetrical internal organs, though... I don't see any in Wells' book, but he tends to show the two halves of the animal at different stages of dissection to show more with one picture. The funnel is also weird, in that in octopus, it's off-center, but I think the development, and maybe even the muscles, form it symmetrically. All octos can switch the funnel to either side, right?
 

DWhatley

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#2
I was wondering about the funnel left-rightedness earlier in the week to know if it would help id an octopus. I tried studying mine but am not sure it stays on one side (I keep forgetting to write it down when I can determine a side to see it it switches).
 

Taollan

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#3
Unless I am mistaken, essentially all shallow water, active octopuses have a highly mobile funnel organ that they can move anywhere in the mantle opening. There is a descent number of octopods with funnel organs that are extensively fused to the mantle, but it seems to me that these are mostly deep water species that tend to be less active, i.e. Haliphron atlanticus and Octopus califonicus. In these octopuses the funnel organ is located medially, and not off to one side or the other. That being said, it would be interesting to see if individual octopuses with highly mobile funnel organs have a preferred side where they keep their funnel, somewhat analogous to right-handed/left-handed in humans. It has been shown that octopuses have a preferred eye.
All of this also makes me wonder if a fused funnel or a free funnel is the developmentally primitive state. Does the funnel separate during development through apoptosis of tissue, like how our fingers separate, or do the funnels fuse later after developing separately?
 

monty

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#4
Taollan;104863 said:
Unless I am mistaken, essentially all shallow water, active octopuses have a highly mobile funnel organ that they can move anywhere in the mantle opening. There is a descent number of octopods with funnel organs that are extensively fused to the mantle, but it seems to me that these are mostly deep water species that tend to be less active, i.e. Haliphron atlanticus and Octopus califonicus. In these octopuses the funnel organ is located medially, and not off to one side or the other. That being said, it would be interesting to see if individual octopuses with highly mobile funnel organs have a preferred side where they keep their funnel, somewhat analogous to right-handed/left-handed in humans. It has been shown that octopuses have a preferred eye.
All of this also makes me wonder if a fused funnel or a free funnel is the developmentally primitive state. Does the funnel separate during development through apoptosis of tissue, like how our fingers separate, or do the funnels fuse later after developing separately?
In nautilus it comes together as sort of two sheets and doesn't completely fuse. I'm pretty sure it's similar in coleoids, but it fuses completely into a tube.

Most of what I know about ceph development is mentioned in this thread: http://www.tonmo.com/community/index.php?threads/8045/

which I think included the origin of the funnel in nautilus in gory detail.
 

pipsquek

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#5
Here's a thought. I always assumed that the funnel was likely to be pointed in the direction of percieved danger, in order to jet directly away from it. That or oriended with a line of escape, which doesn't necessarily have to be in the opposite direction of threat. I would suspect that if they have a preferred eye, then the funnel would be on the same side if there is a "handedness" when threatened and the opposite when feeding. If I'm an octopus, and I see something I want to eat. I have to be able to launch myself at it at some point, so I want to point my funnel directly opposite of my dinner. If I see a threat, then I want to get away from it as quickly and as far as possible with the first blast.

I can't offer any real evidince on this line of thinking. But I remember when I was doing my apprenticeship, my mentor made a few octopuses. Since he never was very good a research, he just looked at pictures. And every picture he looked at had the funnel pointing right at the photographer, so every octopus sculpture he made had two funnels.
 

robyn

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#6
In Nautiluses the funnel folds overlap on different sides in different animals - the left flap is on the outside in some animals and inside in others, and I'm fairly sure it doesn't change over time. It would be interesting to see how it folds during embryogenesis.
 

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