[arpowers]

Reminds of of Project Hail Mary. Never heard the word "carapace" before that book...

[DeathArrow]

In Romanian "carapace" means shell. It seems to mean the same in English, too, but I presume is seldom used: https://en.wikipedia.org/wiki/Carapace

[Symmetry]

It's the biggest solid piece of shell in English. Like the stuff over a crabs pincers is still shell but only the stuff that surrounds the main body is the carapace. Often used as an analogy for other sorts of armor, like a knights breastplate being his carapace or a tank's hull armor.

[drcongo]

It's not uncommon in English, though I suspect it's most often used in technical fields like entomology.

[logicprog]

It's pretty commonly used in my experience, but that might just be the types of books I read perhaps.

[Y_Y]

Carapace is rarely used outside a zoological context, but people may be more familiar with the derived word "scarab", being a beetle with a notable shell. It is unfortunately unrelated to the delicious dish carpaccio, which is named after a man.

[Aachen]

I suspected Brandon Sanderson made it up for his Mistborn series until hearing it in Project Hail Mary also. This is actually why I clicked the thread: was curious if anyone would make the reference!