out of the blue

[esquid]

If this comes to blows my money is on SOS, sorry monty, I'm sensing pent up rage.

 

[DWhatley]

How to cite this page: Maggy Wassilieff and Steve O’Shea. 'Octopus and squid', Te Ara - the Encyclopedia of New Zealand, updated 21-Sep-2007
URL: http://www.teara.govt.nz/EarthSeaAndSky/SeaLife/OctopusAndSquid/en

Steve,
The article mentions benthic cephs eating "polychaete worms" and I recall a member asking what kind of worms they would eat and thought the question odd. Since polychaete refers to a whole host of very different critters, can you shed some light on if the article is referring to bristle worms, feather dusters or some other squiggle that lives in the sand?

 

[monty]

I'll further disrespectfully disagree (seeing I'm the guy that wrote that text on that web site). The web site information is correct; the only real difference (for the sake of those here) between an octopus and squid is that squid have those circular rings and/or hooks arming their suckers. It's a fact. You can support the distinction between the two on the basis of essoteric detail, but it's horses for courses online these days, and 99% of the detail mentioned on TOL goes over the heads of 99% of the teuthologists out there also. Moreover, many of those characters/states cited as diagnostic of squid and/or octopuses are not unique to them (cross-check against the two lists).

I'd bet on SOS over me, too, but I'll ask anyway:

A popular misconception is that squid have eight arms and two long tentacles, while octopus have eight arms and no tentacles. But this is not always the case. The only real difference between the two groups is that squid have hooked or saw-like suckers, and octopus do not.

Are there any octopuses that have anything other than 8 arms? Perhaps this is more of a question of taxonomic versus cladistic classification? My sense is that it's generally agreed that an ancestral form had ten appendages, and vampyromorphs modified arm pair II to filaments, which were then lost in all octopus species. While squids have sucker armament, the article itself mentions later that "All squid possess two long tentacles at some stage of their life." Or perhaps this is a matter of viewpoint: in evaluating a single specimen, the sucker rings and hooks are a great diagnostic criterion, while "8 arms and 2 tentacles" is insufficient for squids that lose their tentacles, so in that sense, I concede. The way I think of the clades, though, is the developmental origins of the arm/tentacle arrangements, and the idea that 8 arms + 2 tentacles at some point in post-hatching development is an important distinctive diagnostic state.

I'll concede that my perspective is probably bogus if you don't like it (and will shift "disrespectfully disagree" to "respectfully question") but I'm curious in what way, because I'm very interested in the developmental control of arm and tentacle arrangements as indicative of phylogeny. It is, of course, also interesting to ask where sucker armament falls in the phylogeny as well. Also, out of curiosity, do cuttles and spirula always, sometimes, or never have sucker rings or hooks? If they don't, but they do have 8 arms and tentacles, doesn't that raise some strange questions about the phylogeny? And, for that matter, since the ancestral belemnites are believed to have had 10 hooked arms without the unusual morphology of feeding tentacles, where should one split the hooked/ringed clades off? Can that be resolved with splitting the 10-armed into 8-armed/arms II filaments->8 armed vs 8-armed/ arms IV 2-tentacled? When did suckers develop relative to hooks, tentacles, etc?

In any case, I bow down to Steve's expertise so I should make it very clear that this is a sophomoric objection, since I want to understand where it's wrong more than claim it's right.

There might be some opportunity for some comment about whether, if an adult human loses his thumbs, whether that makes him likely to be mistaken for an octopus, but that's probably not germane.

 

[DWhatley]

Steve,
Being academically challenged, it still occurs to me as a hobbiest that there is a more basic difference since many forms of octopus can be kept in aquaria but almost no species of squid. This would seem to suggest that there is a considerable difference in the biologics of two beasts.

 

[Steve O'Shea]

Steve,
Being academically challenged, it still occurs to me as a hobbiest that there is a more basic difference since many forms of octopus can be kept in aquaria but almost no species of squid. This would seem to suggest that there is a considerable difference in the biologics of two beasts.

True; there are probably many behavioural and physiological ttributes that differentiate the two groups also, but they're not much use when dealing with a dead animal. Also, only representatives of one of twelve families of octopuses have been kept live in aquaria for any length of time; most of the pelagic and bathyal groups/families have not.

Re all other posts, I'm not arguing with anyone here; it's just the most fundamental difference between both is hooks/rings and not (presence/absence criterion), as opposed to some variable expression of a character state.

Monty, I would have thought that all Sepia and Spirula had sucker rings. Is this not the case?

 

[monty]

True; there are probably many behavioural and physiological ttributes that differentiate the two groups also, but they're not much use when dealing with a dead animal. Also, only representatives of one of twelve families of octopuses have been kept live in aquaria for any length of time; most of the pelagic and bathyal groups/families have not.

Re all other posts, I'm not arguing with anyone here; it's just the most fundamental difference between both is hooks/rings and not (presence/absence criterion), as opposed to some variable expression of a character state.

Monty, I would have thought that all Sepia and Spirula had sucker rings. Is this not the case?

From tolweb, it looks like rings are supposed to be present in all Decapodiformes have rings and stalks. Nixon & Young also shows that, although weirdly, in sepia, the rings are inside the sucker infundibulum rather than on the rim... I didn't mean to say I knew they didn't just that I didn't know if they did...

oops, gotta run... just was mostly curious because I've read some suspicions that ammonites had 2 feeding tentacles, which is hard to reconcile with belemnites and the octo/ deca branching of the coleoids.

 

[octokidwriter]

Dear me, what scientific tornado's have i caused with this simple thread!

Nobody will be surprised however, if i can no longer follow (once again and just keep on wondering how i will explain on paper the difference between octopus and squid to a ten-year-old, having been imposed the limit of not using more than three syllables

thanks for posting the picture of SOS. I now very firmly believe in his existence!

 

[monty]

Dear me, what scientific tornado's have i caused with this simple thread!

Nobody will be surprised however, if i can no longer follow (once again and just keep on wondering how i will explain on paper the difference between octopus and squid to a ten-year-old, having been imposed the limit of not using more than three syllables

thanks for posting the picture of SOS. I now very firmly believe in his existence!

I really admire your desire to be scientifically correct in your ten-year-old's explanations, so I hope we're not driving you nuts with all this. It's a pet peeve of mine that a lot of authors use the "I'm not writing for experts" excuse to write things that are not only simplified, but glaringly wrong. Greg Barord has a signature that says:

"Any scientist who cannot explain his work to an eight year old is a charlatan" --Kurt Vonnegut

and I agree with that sentiment... but I think it's equally important for people who want to pass on that work to the general public make sure to ask enough questions that they "get it."

The point of Steve's and my argument (from my side, anyway) is that although there are general rules to tell squids and cuttlefish from octopuses, the only way to be sure if someone brings you some sort of specimen someone trawled up is to look for rings on the suckers. Since people send Steve such things all the time, but never send me any this is more on his mind than mine*.

To me, who reads a lot of books, I see a bunch of rules like "squids, in general, have eight arms and two longer feeding tentacles, and octos have 8 arms only" and "most squids have fins, while most common octopuses do not," and "most squids and cuttles have an internal stiffening structure (pen or cuttlebone), while most octos do not." There are exceptions to every one of those rules, however, so just following a recipe to decide if something is really a squid or an octo needs to use the most specific rule, the one that Steve likes. I think the 8+2 vs 8 rule is pretty good, and the only exceptions I'm aware of are that some squids lose their tentacles at adulthood, and that the weird Vampyroteuthis infernalis is an evolutionary throwback more related to octopuses than squids, but that has 2 curious feeding filaments.

My preference, when explaining it to someone who doesn't have much background, is to describe the general rules first, mention that they have exceptions, and then that the sucker-ring rule has no exceptions, since I think "ten arms and fins" vs "eight arms and no fins" is a criterion that people can understand quickly, but it's worthwhile explaining that it's not perfect... and this simple version did lead to the newspapers going crazy about the discovery of an "octosquid" that they portrayed as some sort of missing link, when it was merely an unusual squid that had lost its tentacles during capture (not even one of the known species that loses its tentacles naturally)

If I were explaining the difference to a ten year old, I'd tend to say "squids have 8 arms and two long tentacles, but some squids lose their tentacles as the grow up," "squid and octopus both have suckers, but squid suckers have toothed rings or hooks on their suckers," and "most octopuses we see near shore have no fins, but in the deep ocean, there are a lot of octopuses that have fins like squids do."

* edit: yes, I am counting on the people who have access to rotting cephalopod carcasses being too lazy to send them to me just to make a point that sometimes having rotting carcasses sounds better on the internet than it is in real life...

 

[octokidwriter]

Thanks very much, this is really very useful. I think i must seem rather crazy to dig into and then try to write as accurately as possible with no background at all, but then again, i am having such a lot of fun with all this that it is worth while the effort.

 

[monty]

Thanks very much, this is really very useful. I think i must seem rather crazy to dig into and then try to write as accurately as possible with no background at all, but then again, i am having such a lot of fun with all this that it is worth while the effort.

Actually, I think the crazy people are the ones who don't understand that the path to knowing something starts out with not knowing, and then learning...

And anyway, your questions are fun, and the people who are here a lot tend to like to talk about this stuff (the experts who don't tend not to hang around much...)

 

[octokidwriter]

Trying to figure out difference between wonder and mimic octopus, i stumble across this definition, does it make sense:

http://www.downbelow.co.uk/wonderpus .html

Often confused with the Mimic Octopus, this species appears to be very active during the day. Differentiating itself from the mimic it has greater marking definition being a little rustier red and creamier white markings. The wonderpuss has taller eye stalks and is less likely to mimic but does have this ability.

 

[Thales]

Not so much.

Here is a link to some info Crissy posted here a while ago (it vanished here for various reasons, so she gave me permission ot host it)

Welcome to Daisy Hill Cuttle Farm!

They can both be active during the day, however, wunderpus (and I believe the mimic), are more crepuscular most active in the dawn/dusk/night

 

[octokidwriter]

here's some more:

is there any visible difference between "tentacle" and "arm" except for their lenght?

a squid sometimes loses his two tentacles and thus looks like an octopus in some cases, but can he grow them again as well?

how many octopus "species" (is that the correct word?) have already been found up to now, the numbers i find on internet seem to differ a lot?

can the ink of the squid and octopus also be used to create sepia ink?

 

[monty]

here's some more:

is there any visible difference between "tentacle" and "arm" except for their lenght?

Although sometimes they're casually interchangeable, the squid and cuttlefish have two specialized tentacles that are much longer and shaped differently, which they shoot out, much like a chameleon's tongue, with great speed and accuracy, to grab prey. The shape of the tentacles is distinctive, with long shafts that have no (or occasionally a few) suckers, that have muscles optimized for fast striking, and then a "club" at the end of each that has a lot of suckers on a sort of paddle shape, which grabs the food and holds on.

Thales has some great videos of cuttlefish striking with their tentacles on his web site. Google for "daisy hill cuttle farm" and look at the videos.

a squid sometimes loses his two tentacles and thus looks like an octopus in some cases, but can he grow them again as well?

If a squid or octopus loses a tentacle because of an injury, it can grow it back. There are some species in which the tentacles are naturally dropped off at adulthood, and these don't grow back.

how many octopus "species" (is that the correct word?) have already been found up to now, the numbers i find on internet seem to differ a lot?

I don't know, but it's a lot. I can count the species listed in books by Normal or Nesis, but it would take a long time, and I don't think either is complete... Nesis, for example, predates the discovery of wunderpus, mimics, and maybe aculeatus, and Norman's has a lot of "undescribed octopus sp." It doesn't help that it's frequently difficult to determine whether there are several similar species or just one. Steve has a large monograph just attempting to catalog and classify the species of octopuses around New Zealand, and it's 280 pages describing 39 species from that area alone.

can the ink of the squid and octopus also be used to create sepia ink?

Sepia ink is officially cuttlefish ink, but it's similar enough to squid and octopus ink that I'd think any would work. It probably depends on the species. But in general, true "sepia" ink is cephalopod ink of some sort (although I think a lot of what you can buy in a store is imitation.)

 

[octokidwriter]

thanks Monty for the very clear answers. They are very useful. Soon you'll all be writing my books for me
They are in fact two books, i am writing the easiest one now, to get me warmed up for the difficult work. you certainly deserve a copy by now, though it will be Dutch to you, I'm afraid!
got another one: three hearts, any idea why?

Thales has some great videos of cuttlefish striking with their tentacles on his web site. Google for "daisy hill cuttle farm" and look at the videos.

oh, and btw, i can't play those movies, i've already been trying for weeks