out of the blue

[octokidwriter]

Thanks. And now for sth completely different, but more of the same: Argonaut: in wikipedia is described as "a sort of octopus", but is it really?

 

[octokidwriter]

since each sucker has the ability to taste what it touches. ..

does that mean that in fact tasting and touching/feeling are one and the same?

 

[gholland]

Thanks. And now for sth completely different, but more of the same: Argonaut: in wikipedia is described as "a sort of octopus", but is it really?

I think argonauts do fall under the Order Octopoda (Family Argonautidae) whereas chambered nautilus have their own distinct order (Nautiloidia) which is the same level at which squids and cuttlefish are segregated into their own distinct groups. The common name "paper nautilus" is misleading (not unlike many other common names).

 

[Taollan]

Taste and feeling/touch would be distinct sensations. They come from two different type of receptors. Taste comes from what are called "chemoreceptors". When certain chemicals come in contact with a chemoreceptor, the receptor recognizes the chemical and fires off a nerve impulse. Touch is accomplished with mechanoreceptors. They receptors can tell when the tissue they are place in has been moved or deformed and then shoot off a nerve impulse. So at the level of sense reception the two are distinct.
Now that being said, it is really hard to tell what an octopus actually experiences. There are known cases in human where sensations that are collected independently can be fused in brain into a single sensation, or actually be crossed (seeing sounds, or hearing tastes...). It's called synesthesia. So I really have little clue how the sensory information is processed in the octopus brain. I would image however it is something like your tongue. You can both feel the texture of foods, and taste them at the same time, but they are distinct sensations.

 

[monty]

I think argonauts do fall under the Order Octopoda (Family Argonautidae) whereas chambered nautilus have their own distinct order (Nautiloidia) which is the same level at which squids and cuttlefish are segregated into their own distinct groups. The common name "paper nautilus" is misleading (not unlike many other common names).

That's roughly correct, but the "levels" are not quite right. It's detailed at

Cephalopoda

but roughly, the living cephalopods, Class Cephalopoda, are divided into Subclass Nautilodea and Subclass Coleoidea. The genus Nautilus are the only living animals in Nautiloidea, although there are very many fossil representatives. All remaining cephs, including the weird argonauts, Spirula, and Vampyroteuthis, are coleoid cephs, which share a lot of traits in common. In addition to the thick external shell (which, arguably argonauta and spirula might have a claim to) Nautilus has 4 gills rather than 2, and a number of other distinctive differences in anatomy that show that it's only distantly related to other living cephs. The separation between argonauts and other octopus species is way down at the Suborder level, where they're really close to all of the octopuses. For comparison, Vampyroteuthis is part of Superorder Octopodiformes which is in Superclass Coleoidea and distinct from Nautiloidea where Nautilus is found, which is a long way of saying that Argonauta is much more closely related to Vampyroteuthis and all squids, cuttles, and octopuses than it is to Nautilus.

Where this gets really interesting is the debates about where the extinct fossil cephs fall in this picture... there's some evidence that the ammonites, despite having external shells like Nautilus, had a lot more traits in common with the modern coleoids, so the division may be less about having external chambered shells, and more about other things like 2 vs 4 gills, ink sacks, hooks/suckers, number of tentacles, types of eyes, and so forth.

Actually, a much better understanding without all the kooky Linnean Latin endings can be seen in this cladogram:

which I lifted (thanks, Roy!) from the UCMP page here: The Cephalopoda

The splits on that "tree" indicate when the groups diverged from one another (keep in mind that the scale of the tree doesn't imply time, just ordering, but we know that the split at the bottom of the tree happened a very, very long time ago from the fossil record.) So Argonauta are over on the far right, in with the octopoda, while Nautilus and its extinct relatives are on the far left. The splits can be thought of as the "last common ancestor," so the last common ancestor between Nautilus and the argonauts was a very long time ago (between 400 and 500 million years ago), while the last common ancestor between the argonaut and other types of octopuses was (geologically) quite recent.

See also A Broad Brush History of the Cephalopoda - The Cephalopod Page

 

[gholland]

I guess that's what happens when I use an old (and out of date?) reference!

Thanks for setting the record straight Monty! Taxonomy...

 

[monty]

I guess that's what happens when I use an old (and out of date?) reference!

Thanks for setting the record straight Monty! Taxonomy...

If it makes you feel any better, Steve often has to correct me on using the wrong Latin endings and such, and all that was just poorly-digested regurgitation from tolweb and other references... really, just my attempt to make a small step to making the gibberish slightly less incomprehensible to the general public...

I can't keep all of the terminology and structure straight, I can only remember the general big picture to some extent. I stand in awe of the encyclopedic taxonomic knowledge of Steve, Kat, Roy, and other real experts...

 

[octokidwriter]

Hello everyone, i've been a while organising all the information i've amassed so...questioning time again!

- In the article "polarised signaling ...and the p-vision of octopuses"(which btw is very difficult for non-scientific me), two kinds of "polarisation" are spoken of: the polarisation of vision (which is still terribly hard for me to understand, despite of all the effort some of you took to make me see the light , but also "polarised patterns of the skin". Which is not the same as camouflage, as far as i could understand. But then how DO i have to understand this? Something like making oneself invisible?

- Some octopuses have "fluorescent organs"? Are these "organs" or skin? And what exactly do they use it for?

That's it for now. Thanks in advance for the answers!

 

[monty]

Hello everyone, i've been a while organising all the information i've amassed so...questioning time again!

- In the article "polarised signaling ...and the p-vision of octopuses"(which btw is very difficult for non-scientific me), two kinds of "polarisation" are spoken of: the polarisation of vision (which is still terribly hard for me to understand, despite of all the effort some of you took to make me see the light , but also "polarised patterns of the skin". Which is not the same as camouflage, as far as i could understand. But then how DO i have to understand this? Something like making oneself invisible?

- Some octopuses have "fluorescent organs"? Are these "organs" or skin? And what exactly do they use it for?

That's it for now. Thanks in advance for the answers!

1. It sounds like you've mostly got it... polarization is a property of light that, even though it's always there in the light, our eyes don't detect it directly-- we need to use special filters and such to perceive it. For an octopus or cuttle (or a mantis shrimp, or an ant), though, it's as natural to see polarization as it is for us to see color. What they see is a "direction" of polarization. Most often, this is associated with grazing reflections, like the sun off the ocean (which is why fishermen use polarized sunglasses to remove the glare from the water while seeing the fish) but what marine animals usually use them for is seeing outlines of camouflaged animals, like jellyfish, glass squids, and silvery fish that blend into the background. So you can imagine little arrows in the light that define a direction. A lot of light is "randomly polarized," meaning the arrows point all over the place, or it can be "linearly polarized," meaning all of the arrows are lined up with each other. As it turns out, it can also be "circularly polarized" where the arrows follow little helix patterns. Cephalopods don't detect circular as different from random, as far as we know, but they can see the direction of linearly polarized light. Mantis shrimps (stomatopods) can see circular polarization, however.

In the skin case, the skin takes the incoming light, which may be "randomly polarized" and lines up its polarization "arrows" to be "linearly polarized" as its reflected off the skin. Like other skin patterns in cephs, this can be used for displays that are obvious or cryptic... they may want to hide from other animals that can see polarization by trying to hide their silhouettes' polarization, or they may want to make a garish display to catch the attention of a potential mate or intimidate a rival.

2. A lot of cephs do have luminous organs called photophores, but the anatomy varies a lot between species. I think they are usually something like a pocket in or just under the skin, and sometimes (e.g. in Euprymna scolopes) they use symbiotic bacteria to produce the light. Some species have an elaborate reflector and lens system like a projector that directs the light in particular directions, but most have a diffuse glow. Some have eyelid/shutter covers so they can "turn off" their lights, and Vampyroteuthis infernalis has the ability to "ink" a glowing cloud to distract predators as it escapes.

These are used for a number of purposes, although it hasn't been studied enough to know for sure what they all are. Some are used to attract prey or mates... Taningia danae has lights at the ends of each arm that are used to lure and then confuse prey. Many smaller squids use their photophores for "countershading" -- when a predator is below the squid looking up, the light from above makes the outline of the squid clearly visible as a shadow. The countershading photophores light up so that the bottom of the squid is the same brightness as the light coming down from above, rendering it much less visible.

 

[octokidwriter]

thanks for the extensive answer, monty! the more i learn the more astonished i become...

 

[DWhatley]

We will have her keeping one soon. Just to get the correct prospective of course. And maybe book her hero/heroine will be a good guy, sort of a caped crusader so to speak.

 

[octokidwriter]

i'm afraid all of you will be in the book some way or other...you may apply for a favorite role in it, so if you have any preferences, do let me know.

in the mean time: a question to keep up the spirits: read somewhere that ink is toxic and even deadly if the octopus should take it in himself. true?

 

[OB]

If this were the case, I think we wouldn't be eating too much squid ink coloured pasta Are you maybe referring to saliva?

"All Ding’ sind Gift und nichts ohn’ Gift; allein die Dosis macht, dass ein Ding kein Gift ist"

Paracelsus

 

[cthulhu77]

The ink isn't that toxic, but it does burn slightly...more of an irritant than a poison/toxin.

One nice things about octopus, they try to give you a lot of warnings before they actually bite. Having been bitten, I know!

 

[monty]

Perhaps this rumor is because sometimes when an octopus is shipped in a small plastic bag, if it inks it can be a health risk? I believe this is more because the unnaturally high concentration of ink tends to coat the gills so it can't get enough oxygen, so it's sort of like being in a smoky room: the smoke would just be annoying in a large room, but if it were in a small closet, it could get hard to breathe.

Still, it's somewhat in the octo's interest to have the ink be some sort of irritant, and to have it interfere with a predators senses (including sight and smell.) Now that I think about it, perhaps some of the brightly colored, and hence toxic looking, cephs have toxic ink rather than a toxic bite... I wonder if anyone's looked at that...