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Chitinous

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Chitinous

Postby lch2732 » Wed Oct 14, 2009 10:41 pm

What are some disadvantages of having a chitinous exoskeleton?
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Postby JackBean » Thu Oct 15, 2009 12:49 am

Especially, that it can't grow with you, so you must change ;) And at that time you are especially vulnerable

BTW do you, someone, know, how these animals work, when are they changing? I mean, the exoskeleton is their only support, right? So if they take it off and wait untill new is formed, how can they move or anything?
http://www.biolib.cz/en/main/

Cis or trans? That's what matters.
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Re:

Postby biohazard » Thu Oct 15, 2009 6:43 am

JackBean wrote:BTW do you, someone, know, how these animals work, when are they changing? I mean, the exoskeleton is their only support, right? So if they take it off and wait untill new is formed, how can they move or anything?


Afaik this depends on the animal in question. Some insects, for example, do not grow in size at all when adults and thus avoid this problem. Animals that do shed their exoskeleton can move, the underlying soft exoskeletong along with the internal pressure of the animal are enough to facilitate this. But at least many crayfish (and likewise many otehr arthropods that shed their exoskeleton) hide until their exoskeleton has hardened again - that is, they can move, but will not unless they really have to. They just hide in some nook and wait.

And what comes to other disadvantages of chitious exoskeleton: it allows muscles to attach only inside of the exoskeleton, quite unlike human muscles for example work. This provides poorer strength production, which is why arthropods cannot really grow much larger than what we see around us. For similar reasons, virtually all the largest arthropods live in water, because there you need less strength to move heavy weights.

Even though we know that ants are mighty strong compared to their size, human-sized ants would collapse even udner their own weight and they could not carry a hundred or so times their weight like small ants do!
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Postby Darby » Wed Oct 21, 2009 10:33 pm

Actually, leverage around the inside of the tubes should be better than on the outside, which is part of the reason that arthropods have great proportional strength. It's the weight of an all-on-the-surface skeletal system that is the main size restriction.
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Re:

Postby biohazard » Thu Oct 22, 2009 7:36 am

Darby wrote:Actually, leverage around the inside of the tubes should be better than on the outside, which is part of the reason that arthropods have great proportional strength. It's the weight of an all-on-the-surface skeletal system that is the main size restriction.


Hmmh, I think you're right. Thanks for the correction. It certainly makes sense, but still I somehow managed to get it the other way round. I just had (and still have) this odd recollection that the size limitation was due to some sort of disadvantage in the muscle attachment inside the skeleton when compared to outside. I try to find out what this thing was, because now it's bothering me! :P
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Postby biohazard » Thu Oct 22, 2009 7:48 am

Okay, as it turns out I remembered it wrong:

The muscle attachment inside the skeleton is indeed more efficient than the human way of attaching outside. But because the exoskeleton is much heavier than an internal one, its weigth increases proportionally: the bigger the arthropod, even heavier the exoskeleton - and soon it gets heavier than there is availbale space for additional muscle and thus the whole animal would become too cumbersome and eventually collapse under its own weight, despite the relatively strong muscles.

"Since a two-fold increase in body length typically results in a four-fold increase in surface area and an eight-fold increase in volume and mass, there is an upper limit to how large insects can become (somewhere around 125-150 grams). Beyond this size, the insect's surface area is just too small for attachment of all the additional muscle tissue."

http://www.cals.ncsu.edu/course/ent425/ ... ccess.html

Maybe it was this lack of surface are that I was thinking of as "weak" muscles!

Additionally, I found out, the circulation and respiration systems seem to play a major part: the bigger the animal, the bigger portion of its body cavity needs to be reserved for tracheal tubes, and eventually there is not enough room for big enough tubes. Thus, there were giant insects millions of years ago, when there was also more atmospheric oxygen and as such smaller tracheal tubes would suffice. That is why, along with the weight, I guess marine arthropods are much larger: they use gills and the water supports their heavy exoskeletons.

Hope I got it right this time! :O
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Re: Chitinous

Postby Chroma » Sat Oct 24, 2009 7:25 pm

Sounds right on everything that I've seen (which doesn't cover half of what you put).

I know a large portion of arthropod deaths occur during molting, so having to shed it is a definite drawback, but given the distribution of arthropods, saying its still a net benefit is an huge understatement.

I also was shown from some over-simplistic scale-factor ratios if we were shrank down to the size of an ant, we would be many times stronger then they were, but would not be able to eat enough to supply the energy requirements that would be necessary. Unrealistic and useless but interesting anyways...
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