Differences between crayfish and spiders.

Insects usually have a pair of antennae. Most crustaceans do not have antennae. Insects usually have mandibles for breaking food, which aid in food digestion. Crustaceans have chelicerae, or claws, at the end of their first set of legs for the same purpose.

Insects are found in almost all ecosystems on Earth, and the ocean is rare. Crustaceans are commonly found in water – and usually in oceanic regions. Having adapted to their habitat, many species of insects have developed wings – two pairs for the majority and one pair for the minority. The tracheal system is also intended for breathing. On the other hand, crustaceans breathe using gill mechanisms.