size of arthropods

[cambrian_exp]

i would like to ask that can arthropods become as large as humans? or elephants? . what if all the chordates ancestors were wiped out during cambrian era , then did arthropods would have produced some large creatures or an intelligent creature? if u have any web link on this topic then post it

[Mokele]

No, their size is pretty much set at the moment. Two of the main problems are that an exoskeleton limits the surface area in contact with the outside world, and therefore restricts respiration, and that arthropods must molt. When an arthropod molts, it develops a new but soft exoskeleton, then sheds the old. Upon emerging from the old one, it it soft and pliable, and must immediately inflate itself before the exoskeleton hardens from contact with the air. Once it does, the insect cannot grow any more until next molt. This is fine at small sizes or when supported by water, but a truly large, terrestrial arthropod would run into big trouble.

 

That said, they used to be larger, back during the Carboniferous, when the atmospheric O2 levels were much higher. By 'larger' I mean dragonflies with 2 foot wingspans, spiders the size of footballs, and 6 foot long millipedes.

 

Mokele

[cambrian_exp]

but spider and dragonflies dont have exoskeleton? then why cant they grow upto 3-4 metres and i know of largest arthropod which lived during silurian times, it was sea scoropian that grew up to 1.2 metres. cant these creature produce intellegence? and what abt mollusks? i mean mostly all invertebrates are small. none of them matches the dinosaurs and mammals and birds.

[Daecon]

Any creature that dosn't have an internal (endo)skeleton has an exoskeleton, spiders, insects... I'm not sure, but I imagine that's also true for for crab and lobster and other seafood (except fish, obviously)?

[Skye]

Japanese spider crabs!

[Daecon]

*is gonna have nightmares tonight*

[Halucigenia]

*is gonna have More[/b'] nightmares tonight*

Giant isopod

[Daecon]

Hehe, that one's quite cute. Looks like a giant woodlouse.

 

But that freakin' huge spider shaped crab? Gives me chills and makes my skin crawl just to think about it!

 

[EDIT: After posting this message, I went and read the text below the picture, "Their morphology is nonetheless familiar to most people as giant isopods closely resemble their terrestrial cousins, the woodlice..." ]

[Halucigenia]

After posting this message, I went and read the text below the picture, "Their morphology is nonetheless familiar to most people as giant isopods closely resemble their terrestrial cousins, the woodlice..." ]

Yea, just imagine them crawling about your living room after dark

[Kermit]

Yea, just imagine them crawling about your living room after dark

 

Great. Reinforce my phobia of insects. Agh.

[AzurePhoenix]

Not insects. Isopods. See? No more fear!

[Daecon]

I could imagine it lying on it's shell wanting me to tickle it's tummy...

[cambrian_exp]

well i got this forums idea from a tv programme called origins which told what would have happened if chordates losed evolutionary battle with arthropods during cambrian exp

[Skye]

The exoskeleton could simply become internal, as in some cephalopods. The intelligence would likely require cephalisation of the nervous sytem, although it's difficult say that's necessary, at the very least it would help if their brain wasn't wrapped around their throat. The gas exchange isn't such a problem because some arthropods have some form of gills (crustacea) or lungs (arachnids).

[rakuenso]

war of the worlds isopod.. yup

 

how do those things mate, from the picture of the underside on wiki, i didn't exactly see a.. well you get the idea.

[Skye]

Probably happens during the females moult, like with similar crustacea.

[Mokele]

but spider and dragonflies dont have exoskeleton?

 

Yep, all arthropods do, including them. It was just less of a limitation back then.

 

Any creature that dosn't have an internal (endo)skeleton has an exoskeleton, spiders, insects... I'm not sure, but I imagine that's also true for for crab and lobster and other seafood (except fish, obviously)?

 

Actually, far from it. A good many organisms, like worms and octopi, have hydrostatic skeletons, in which their bodies are supported by fluid-filled spaces. Compression of these spaces causes them to extend in the non-compressed dimension, like a long balloon when you squeeze it, which it how octopi shoot out their tentacles.

 

The gas exchange isn't such a problem because some arthropods have some form of gills (crustacea) or lungs (arachnids).

 

Yes and no, as the lungs are still very simple and inefficient, which limits size.

 

Mokele

[Daecon]

how do those things mate' date=' from the picture of the underside on wiki, i didn't exactly see a.. well you get the idea.[/quote']

 

Are you sure? I was fairly sure that part of his anatomy was pretty obvious. Unless my knowledge of giant woodlouse anatomy is wrong...