Decapods

Scientific name : Decapoda

Decapods have 5 main couples of legs. Four are normally used for walking, the first is transformed into claws, useful to manipulate objects, to cut or break.
The shell (or exoskeleton) must be replaced during growth, this process is named molting.
Crabs are a suborder of decapoda, scientifically named Brachyura (small tail).