It's probably nothing buuuut....

monty

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sensory strategies

This is sort of a "chicken and egg" comment with respect to evolution, but it occurs to me that the decapods are primarily visual hunters, and while octopi certainly have well-developed vision, they place a good deal more emphasis on tactile interaction with their environments, including a lot of sticking of arms into places they can't see. Perhaps the "shoot out tentacles" approach is coincident with the strong visual component to the squid and cuttle lifestyle? Of course, I imagine that open-water octopods are less tactile than the benthic ones, although the "inside-out" behavior of vampyroteuthis suggests to me that it has a tactile component to its hunting despite not being near nooks and crannies... I also recall that the optic lobes on squid brains are much much bigger than octopuses, although I don't know about non-benthic octopuses...

just another random thought...
 


Graeme

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Vampyroteuthis said:
My thoughts are: the prescense/abscense of tentacles depend on where they hunt. Octopi normally hunt on the ocean floor, among rocks and such, so wouldnt long tentacles just get in the way? Squids on the other hand, hunt more in the open, where a pair of elasticy fish catchers would be quite handy.
Rambling on with just a hunch..

Exactly what I thought dude.

OK, I've been racking my brain trying to think up another question, it's up to you guys which one you wanna answer, I'm just trying to come up with interesting discussion points on a regular basis (I've been on forums where a couple of people have done this, and it seemed to get quite good; started getting into really deep philosophical stuff, which isn't bad for an "anime forum":lol:).

So next question: There are, I think, 2 species of Octopus in NZ left with a vestigial "shell" which is referred to a Pen. Now, why would the pen still be present in these 2 species when it's not in others? Could it be the same idea of the vestigial pelvis in certain Cetaceans? Could these 2 species just be elvolving a little later than most octopuses? Or could it be possible that they sevre a cartain purpose, like keeping structure, or protection (eg. Bistle-nose Catfish has barbs that stick in the predator's throat)?

Graeme
 

Steve O'Shea

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Graeme said:
So next question: There are, I think, 2 species of Octopus in NZ left with a vestigial "shell" which is referred to a Pen. Now, why would the pen still be present in these 2 species when it's not in others?

Hi Graeme. There are nine species here (in NZ) with the shell vestige you refer to (3 x Opisthoteuthis spp.; 1 x Cirroctopus sp.; 1 x Luteuthis sp.; 1 x Grimpoteuthis sp.; 1 x 'Cirrothauma' sp.; 1 x Enigmatiteuthis sp.; 1 x Cirroteuthis sp.; each has a name/as in it is described). These are all cirrate octopuses, the most primitive (or basal; depends if you want to attribute polarity to the group), all of which (with a global distribution) possess the shell vestige (and fins). Octopodids (conventional benthic octopuses) also have a shell vestige, but this is further reduced in this group and takes the form of 2 spindle-shapped structures in the mantle called stylets.

Being a shell vestige - a structure slowly being phased out over the course of time - they needn't serve any purpose. In cirrates they do provide a hard structure that the muscular fins can anchor to; in incirrates (inclusive octopodids) their 'function' is a little more obscure. They are rather poorly studied structures.
Cheers, Me
 

Graeme

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Ah! So it is kind of like the Cetacean pelvic bone! You know, not long after I posted, I wondered if it was 9, but I couldn't find the reference, which I found last year for uni work, so I thought I should leave it, in case I made a complete bampot of myself (looks like I kinda did anyway!).
Thanks for that.
 

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