They exchange gases through pores in the skin--a fairly common process for things with cuticles https://journals.biologists.com/jeb/article/221/8/jeb177568/335

They exchange gases through pores in the skin--a fairly common process for things with cuticles https://journals.biologists.com/jeb/article/221/8/jeb177568/335/Cuticular-gas-exchange-by-Antarctic-sea-spiders https://journals.biologists.com/jeb/article/221/8/jeb177568/... https://en.wikipedia.org/wiki/Cutaneous_respiration https://en.wikipedia.org/wiki/Cutaneous_respiration