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I am trying to imagine a scenario where, on an abandoned terraformed planet, decapod crustaceans (more specifically, carideans such as shrimp) evolve lungs and colonise the land as insects have done. However, possessing lungs, they can grow to far larger sizes, with the largest growing to the size of moose, (but no larger because of their exoskeleton’s weight limit).

What I am bothered about is this: how could a crustacean evolve lungs? Seeing as they lack swim bladders and therefore having nothing for lungs to evolve from.

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    $\begingroup$ How did spiders evolve lungs? How did snails evolve lungs? $\endgroup$
    – AlexP
    Nov 27, 2022 at 21:37
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    $\begingroup$ @AlexP fun fact: most arthropods have what is known as an Open circulatory system, meaning that air is just absorbed passively by the body and not actively pumped through the body. I should know. $\endgroup$ Nov 28, 2022 at 0:05
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    $\begingroup$ @redfrogcrab: Yes, most arthropods have what is known as an Open circulatory system, meaning that their haemolymph is not used as an oxygen transport system, and they use other means to transport the oxygen to the tissues. (And at least some of them do actively ventilate their tracheae.) The spiders and scorpions which have lyngs, however, do use their blood to carry oxygen, utilizing (AFAIK) haemocyanin for this purpose; and they do have hearts which do pump the blood. $\endgroup$
    – AlexP
    Nov 28, 2022 at 0:14
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    $\begingroup$ I'm delighted that you received a practical answer. But please be aware, it is not the intent of Stack Exchange to replace the process of education. Explaining how anything could evolve would violate the help center book rule in spades. You basically asked us to provide, what, two years of education? I suspect this question was better suited for Biology. $\endgroup$
    – JBH
    Nov 28, 2022 at 2:26
  • $\begingroup$ What's wrong with treating crustaceans as arthropods? $\endgroup$
    – DKNguyen
    Nov 28, 2022 at 18:40

1 Answer 1

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Crustacean lungs have already evolved. This is a solved problem, as there are already numerous air breathing crab species, such as coconut and hermit crabs.

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    $\begingroup$ Evolved more than once, too: various arachnids use book lungs. $\endgroup$ Nov 28, 2022 at 11:26
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    $\begingroup$ @StarfishPrime: Unlike insects, arachnids are not descended from crustaceans. $\endgroup$
    – AlexP
    Nov 28, 2022 at 13:40

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