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Is it possible for an animal to have isolated air-spaces like a nautilus or man o' war if it also has lungs? The lungs need not be for breathing, but they should be directly connected to some air-collecting orifice. The air-space must be filled with air or gas, but otherwise could be anything plausible

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  • $\begingroup$ Do humans with their lungs and intestinal gas count? Does the gas in the stomachs of ruminants count? On the other hand, many fish (called "physoclist" ) have no connection between their swim bladders and the alimentary canal -- the gas inside is regulated by other means and it is different from atmospheric air. $\endgroup$
    – AlexP
    May 16 at 19:18
  • $\begingroup$ @AlexP The stomach and intestines are connected to the outside world and can accept matter directly from the environment, so they don't count as enclosed air-space for my purposes. Physoclist fish, while they have an enclosed air-space, they don't have lungs or another exposed air-space $\endgroup$ May 16 at 19:34
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I can think of two ways

1:1 bilateral asymmetry

the animal has one lung and one swim bladder, snakes can work with one lung, as long as you make it beg enough a single functional lung works. whether the pair started as swim bladders or lungs is up to you. basically the lft os one thing and the right is another. organisms already did something similar with the circulatory system to create a four chambered heart.

Air sacs

Your thing evolved from something like birds that have many air sacs as well as lungs, then it turns one set of air sacs into swim bladders. Note such a creature will not have gills, air sacs are a fairly advanced breathing mechanism. Birds haven't become fully aquatic because hard shelled eggs are incompatible with ovoviviparity, so you likely can't use actual birds but there is no reason an alien creature could not evolve it. shelled eggs and air sacs are not linked in any way.

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What you are asking is basically a swim bladder in an organism that doesn't necessarily swim.

The swim bladder, gas bladder, fish maw, or air bladder is an internal gas-filled organ [...]. The swim bladder is evolutionarily homologous to the lungs. Charles Darwin remarked upon this in On the Origin of Species. Darwin reasoned that the lung in air-breathing vertebrates had derived from a more primitive swim bladder.

It can be derived from a lung which can be filled or emptied by exchanging gas on request.

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  • $\begingroup$ The question never states that the creature must be terrestrial, just that it has some sort of lung. Also, the question states (or at least implies) that there should be multiple spaces, with at least one of them enclosed completely, and at least one of them that can be opened to the environment $\endgroup$ May 16 at 18:02
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    $\begingroup$ @IchthysKing then his answer is still valid. The examples in this subcategory show that it is certainly possible, while giving no reason it cannot be implemented in a different subcategory. $\endgroup$
    – Trioxidane
    May 17 at 7:07
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There's really no point. Lungs essentially perform the same role as a swim bladder (indeed, they're the same organ in fishes), and lungs originally evolved as a buoyancy organ and only secondarily became used for oxygen exchange. All a lung is is an "isolated air space" that has a moist cutaneous lining for gas exchange.

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    $\begingroup$ Lungs aren't isolated, as they can be emptied and refilled with external air. Furthermore, lungs must be filled with air (or some other natural substance), whereas an isolated air space could contain a novel mixture, as in the man o' war $\endgroup$ May 16 at 18:07
  • $\begingroup$ @IchthysKing There are multiple types of swim bladders. Physostomous fish have a direct connection between the swim bladder and the alimentary canal and thus refill their swim bladders by gulping air. Physoclistous fishes have secondarily severed this connection and must refill their swim bladders using gasses extracted from the blood stream. The latter is basically what you are describing. $\endgroup$ May 17 at 3:23
  • $\begingroup$ The question asks if both sorts of swim-bladder (or similar structures) could coexist in a single animal $\endgroup$ May 17 at 7:27

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