mushi 虫

insect or bug, but also crustaceans, mollusks, arachnids (spiders), reptiles, amphibians, etc. so basically any animal that is not a mammal, bird or fish. Often refers to some particular animals like moths, beetles or whatever insect they don't know the name of.

The kanji "mushi" is common among shellfish, crabs, etc. But the kanji 魚 "sakana" (fish) also has a wider meaning than just fish, as it is extended to whales too.