There are 5 families and more than 400 species of crayfish, mainly living in fresh water. Among them, crayfish family and saw crayfish family are marine types. The front edge of the head breastplate heals with the anterior plate of the mouth, the ventral armor of the last thoracic segment heals with the anterior segment, and the basal segment and seat segment of the second to fifth pairs of feet do not heal. Although the number of species is small, some species have important economic value.
Under natural conditions, crayfish like to live in water bodies with flowing water, high dissolved oxygen content, high transparency and fresh water quality. Almost all crayfish live in fresh water, only a few in salty fresh water or salt water. It is often hidden under the stones of streams and lakes and active at night. It mainly preys on snails, insect larvae, worms and tadpoles, and some eat plants.