system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do crabs, or any crustacean in fact, breathe on both land and in water.
gpt
Not all crustaceans are capable of doing this. Some are exclusively aquatic, some are exclusively terrestrial, and some can be on both land and in water with different degrees of comfort in either place. For land crustaceans or crustaceans that can live in both land and water, the key is keeping their gills wet. As long as the gills are wet, oxygen in the atmosphere comes in contact with the moisture on the gill and then the gill extracts that oxygen. They can keep their gills most by going into some body of water to wet them, keeping them moist with atmospheric humidity, or by excreting water from their bodies.