Why crabs are not insect?

Crabs are not insects, they are crustaceans. Insects and crustaceans are both arthropods, but they belong to different classes. Insects have six legs, three body regions (head, thorax, and abdomen), and one pair of antennae. Crustaceans have ten legs, two pairs of antennae, and their bodies are divided into two regions (cephalothorax and abdomen).

Crabs are crustaceans. They have ten legs, two pairs of antennae, and their bodies are divided into two regions (cephalothorax and abdomen). They also have a hard exoskeleton made of calcium carbonate. Crabs are found in all oceans and some freshwater habitats. There are over 4,500 species of crabs, and they come in all different shapes and sizes. Some crabs are very small, while others can grow to be quite large. The largest crab species is the Japanese spider crab, which can have a leg span of over 12 feet.