I know that practially all other terrestrial invertebrates are inherently limited in size, primarily by their exoskeletons, and by their respiratory systems, which impose upper thresholds on their maximum sizes depending upon oxygen levels. But is the same true of air-breathing land molluscs? In the oceans, all of the largest, most massive invertebrates to have ever existed have all been molluscs. Other than competition, and predation, is there anything preventing the hypothetical evolution of gastropods the size of the very largest cephalods, like giant squids?

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    $\begingroup$ Blue whale 30 metres / 190 tons; Colossal squid: 14 metres / 750 kilograms. You'd expect them to be lightweight when they have no bones, but their length is pathetic, too, especially for something that's supposed to be mostly just arms. $\endgroup$ – John Dvorak Jun 22 '18 at 2:45
  • $\begingroup$ While I know you've stated 'other than ... predation', it's important not to discount the problem that would represent to a giant gastropod. They're not all that mobile at their current sizes, so at larger sizes they represent a cheap (energy wise) food supply that's a lot harder to hide and protect from the elements as well for that matter. $\endgroup$ – Tim B II Jun 22 '18 at 3:43
  • $\begingroup$ You might be interested in the Desert Hopper, from The Future is Wild, so you could search that up. By the way, that show's a bit outdated, but here's a similar beast drawn by the paleoartist and speculative evolutionist Joschua Knuppe; pbs.twimg.com/media/Dewn_9MX0AAmRmu.jpg . That one should be fairly plausible. $\endgroup$ – SealBoi Jun 23 '18 at 18:19

Other than competition, and predation

When you are on land you cannot rely on hydrostatic to hold your body. And with no skeleton (endo or exo that it be), I have an hard time imagining a large sized gastropod moving around without collapsing under its own weight.

Aside from Jabba, being a fictional character, the largest slug and the largest snail on earth are rather small (but still somehow yuk)

enter image description here enter image description here

  • $\begingroup$ Technically, Jabba was a slug (no shell) $\endgroup$ – nzaman Jun 22 '18 at 5:27
  • $\begingroup$ @nzaman, added that $\endgroup$ – L.Dutch - Reinstate Monica Jun 22 '18 at 5:33
  • $\begingroup$ I was under the impression that larger snails existed, but this is indeed the largest one. $\endgroup$ – Renan Jun 22 '18 at 17:10

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