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Re: How large insects may have come about

2011/9/19 David Marjanovic <david.marjanovic@gmx.at>:

> All primarily aquatic arthropods have gills which transfer oxygen to the
> blood (hemolymph). Unlike the air in tracheae, blood is actively
> transported, so size doesn't matter.

Active transport may be an advantage to deliver oxygen, but this would
not explain the size difference between marine crustaceans or
merostomatans on one side and Recent arachnids on the other. I would
expect that if oxygen acquisition is what impedes arthropods from
growing larger, arachnids would be in principle able to grow larger
than crustaceans because of living in an environment with greater
concentration of O2.