Today I learned

Beware: the true isopod pillbug should not be confused with the astonishingly similar pill millipede! The pill millipede is (obviously) a millipede, not a crustacean at all! However, it not only looks like one — it eats the same stuff, namely decaying plant matter.

(Most millipedes eat decaying plant matter. Most centipedes, though, eat insects, worms, and such — although there's a giant one in Brazil that goes for mice and smallish birds. Eep.)