Since this word is made up of a single kanji, it probably uses the kun'yomi reading. You did not learn this reading, so here's a mnemonic to help you:
Shells come from (から) living animals. You can't have a shell — or a carapace (から) — unless something was once in there. They have to come from something.
This word isn't limited to animal shells though! It covers seed shells, or husks, too. 🌱
Please put crab shells on this plate.
What do we do after removing the husks from wheat?
I watched a video that captured the moment when a seed breaks through its shell and sprouts.