Meanwhile, the author squats in another corner, deeply regretting asking a local semi-expert how biologically plausible the Klaxes are.
How implausible are they? Let me count the ways...
1: You ain't going to get a fully exoskeletal body that large.
1a: It's too heavy.
1b: That much shell is too energy-expensive. (This is gonna be a theme.)
1c: Shedding and regrowth is a major issue. Sloughing off half your body as a large animal just ain't going to work.
1d: Large animals need circulatory systems if they're going to exert any degree of sustained effort.
1e: Large animals need lots of calories. Assuming Klaxes aren't eating continuously, that means they eat meat, they eat a lot of it at once, and then they digest it over an extended period. That means they need space to store meat they're digesting inside their shell, unless they want their internal organs to be squashed.
2: Their legs can't look like that.
2a: That low, crablike posture with sideways-splayed limbs? Aquatic feature, born of an environment where you don't have to support your own weight and can swim around. Terrestrial animals have taller, more forward-facing limbs so they can step over things.
2b: Limbs of large animals are very energetically expensive, so they ain't gonna have ten of them.
Note: You can see both of these in the coconut crab. While it technically does still have ten limbs, only six are large enough to look like limbs at a distance. The forward legs are also angled further towards the front of the crab, and elongated.
3: They need better manipulators than pincers.
3a: How are they managing fine manipulation without fingers?
3b: How are they managing to get sensitive tactile feedback with shell-enclosed pincers?
4: Where are they getting the energy budget for all this?
4a: Large brains, hardened shells, and multiple limbs are all expensive.
4b: But if you just make calorie-dense food readily abundant, intelligence stops being a competitive advantage, and is never selected for. (Large brains are expensive!)
4c: And if your answer to this is "they cook their food", may I remind you that this is an aquatic species you're describing?
My answers so far:
1a: Their planet has slightly lighter gravity than earth's. (I don't want to go too far or their ecology will start getting really unrecognizable really fast, but I'm okay with allowing a leeway of maybe 10%.)
1b: Okay, they're only partially exoskeletal: there's bony endoskeleton in the limbs. (Like turtles!)
1c: They start out relatively soft and squishy and harden over time, like coconut crabs do. Molts happen late in life, and aren't naturally selected against because Klaxes reproduced decades before then in the ancestral environment.
1d: Okay, they have circulatory systems, but they still use hemocyanin because it's more efficient in the lower oxygen pressures and colder temperatures of their homeworld.
1e: Not a huge issue, especially because of 1c's answer.
2: Okay, they emulate coconut crabs. Not a huge concession: they still look acceptably crablike.
3a: Okay, they use those two reduced pairs of forelimbs for fine manipulation very close up. There's some precedent for this in the fact that coconut crabs use a reduced pair of forelimbs to grab and hold on to coconut shells, using them for protection while they're still young and squishy.
3b: The specialized manipulator forelimbs are unarmored. Also, Klaxes have better eyesight and a better sense of smell than us.
4: We've addressed the limb-count issue, and the shell is a one-time investment as far as evolution is concerned: so that leaves the brain-size issue and the cooking issue.
My answer to that is: why are we assuming that energy expenditure and intelligence have a 1:1 correlation? The field of avian neurology suggests that the human brain may actually be surprisingly inefficient compared to other possible designs. I don't have an issue with assuming that wiggle room is large enough to contain the Klaxes.
Still, this does mean the Klaxes' metabolic budget is pretty strained overall, between the shell, the brain and the extra limbs. That pretty much obliges them to be hypercarnivores, getting the majority of their energy from calorie-dense meat. In other words: they're pastoralists, not farmers.
This noticeably changes the flavour writeup and Tech Deck belonged to for "terrestrial agriculture", because it would actually represent a dedicated domestication project as the Klaxes learn how to ranch. I'll put that tech in the Biology deck, and edit the description of the current one to focus on tree farming for wood.
As for cooking reducing the amount of energy needed for digestion: yes, fair, fire does predigest things for us. But we eat many uncooked foods, and have many processes for predigesting things. The one that springs to mind as being relatively easy to achieve in an aquatic environment is fermentation, which says pungent things about the state of modern Klaxes cuisine.
