New Thread ;-) - Cephalopod Fact Check

tonmo

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#1
Welcome to our new forum, Cephalopod Fact Check! DWhatley is Moderator; thanks to Level_Head for the idea! This is the place where we can debunk common myths and reinforce facts. For example, my pet peeve, jumbo squid vs. giant squid; this is consistently messed up by local West Coast newspaper outlets.

Keep in mind that if you endeavor to claim a fact, we'll ask that you back it up with proper reference.

TONMO.com: keepin' it real. :read: :grad:
 

nevergirl86

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#2
On occasion, while explaining something cephy to someone and I use the term "arms", they usually attempt to correct me and say "tentacles". When I am then asked to explain the difference...well...that's where I need some help! I have read that in comparison to squid, I know that arms have suckers on the whole length, whereas tentacles have suckers at just the tips. But can anyone provide me with a better clarification and way to explain it to a ceph layman?
 

DWhatley

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#3
If you look up the definitions of tentacles, you will find that they incorporate both the idea of reaching out and grabbing as well as locomotion and exploring. However, in the case of cephalopods we consider appendages of locomotion and exploring different from appendages that are solely used to capture prey. I am not sure if there is an official definition but basic knowledge of the anatomy of the decapods vs octopods reveals a distinct difference in both function and physical makeup between arms and tentacles.

Visually, we make the distinction that arms have suckers along the whole length where tentacles are either suckerless or end in a suckered club. So visually, squid and cuttlefish have 8 arms and two tentacles, octopuses have 8 arms and nautilus have only tentacles.

Functionally, squid and cuttles have two specialized arms used solely to capture prey (or is that 8 specialized tentacles :biggrin2:). The two tentacles can be launched at high speed and clasped together, something the arms can't do. The 8 arms are used for locomotion and manipulation of food once it has been brought to the the mouth area. Octopuses have only 8 appendages that all appear and are used generally in the same manner. Instead of tentacles to catch moving prey, they pounce and trap their meal, again using their arms to hold and manipulate the captured food (there is some speculation that the front 6 are more arm like and the back 2 more leg like in use. This thought was a recent outcome of a citizen-scientist observation project that was initiated to see if it was worth studying left and right favoring. The mass observations pretty well nixed any future study on the right/left armed thought but suggested the front/back useage differences. You will note that the summary article says "tentacles" :roll:). There probably isn't anything high speed about the nautilus but it does use its tentacles for snaring food and only marginally for moving about.

Soooo ... octopuses vs octopi vs octopodes or arms vs tentacles vs legs all are probably technically acceptable but there is a preferred usage in both cases and our ectrentic interest allows some latitude for snobbery :wink:
 

DWhatley

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#4
Tony,
I'm WHAT? For 3 years I did not know I had this assignment! :roll:
 

Mot Reyd

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#5
Having the Octopi, octopuses and octopodes argument with countless people has slowly made me just accept that people will only believe what they want
Despite me sighing myself into oblivion as they try to tell me incorrect facts
 

DWhatley

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#7
Mot, for those people just use octopodes (see the Webster video at the top of this thread for the pronunciation - I was way off - if you are unsure, love this video). It is esoteric enough to end the argument.
 

tonmo

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#12
It's funny, this USED to be a forum, but when we consolidated forums earlier this year, we just folded it into Physiology and Biology. There weren't too many threads in the forum. So I will rename this to the Fact Check Thread! :smile:
 

DWhatley

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#13
Interesting Octopus Fact: The diet of the whiskery shark consists almost entirely of octopuses

Source Wikipedia I ran across a similar note in a googled excerpt from a shark paper that was not available without subscription so I looked for another source that restated the information.
 

OB

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#14
An interesting fact to come out of Greg Barord's field research, is that nautilus is most likely predominantly a scavenger, placing different requirements on its arms/tentacles...
 

Jean

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#15

DWhatley

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#16
Indeed, that is unfair Jean since so many of the publications are not available for free reading (your direct reference is AU $25 just to read, the excerpt displayed in my Google scan did not even include the information of interest in the Abstract). Much of the content on Wikipedia does give references for content like this and they work hard at marking information that is not officially referenced (especially for the sciences). If students are not allowed to actually site Wikipedia, at least mention that it provides a place to find actual material sources for a topic. For everyday, quick reference use (often leading to rabbit trailing), I find it indispensable and use it for definitions almost daily.
 

Jean

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#17
Ah yes but our Uni pays for access to many of those journals etc! We are aiming for RIGOUROUS research and sorry, much on wikipedia is just not, yes it can lead to peer reviewed work and that's Ok wikipedia as a primary source is not. BTW not my rules although I tend to agree with them PLUS our students can actually VISIT the library who will either have hard copies or have them available on a computer kiosk! I was trying to be tongue in cheek......guess it didn't come off! :biggrin2:
 

DWhatley

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#18
I guess I think it is unfair to Wikipedia to NOT site it as a place to find deeper material. I am not suggesting that it is a scientific reference source but it is far easier to use than a card catalog for locating information on parts of topics (ie if you are looking for something about squid suckers or what they eat or what eats them) and it stays fairly current. Some papers do a good job at placing topic points in the abstract but many do not.

However, THIS is ridiculous:
http://www.ebay.com/sch/i.html?_odk...3.TR0.TRC0.XOctopoda&_nkw=Octopoda&_sacat=267

Almost all the "books" are articles from Wikipedia
 
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