There are approximately five classes. Only three were considered in BIO 5. The Class Crustacea includes crayfish, lobsters, crab, and barnacles. Most of these animals live in an aquatic environment. The Class Arachnida includes spiders ticks and scorpions.
Insects are the largest group of animals in the Kingdom Animalia.
Animals included in this Class are flies, bees, termintes, fleas, butterflies, beetles, etc. The Class Insecta has three tagmata, three pairs of walking legs, most have two pairs of wings, and one pair of antennae.