Crayfish swimmerets are appendages on the ventral side of the crawfish's abdomen. The pair that is closest to the abdomen shows the sex of the crayfish.
The swimmerets on males are used to transfer sperm to the female's oviducts. The swimmerets of a female crayfish are soft and used to carry the eggs or newborn. Swimmerets are also used to make water currents. The crayfish's body is split up in two parts, which are the abdomen and cephalothorax. The cephalothorax has 13 different areas and a pair of appendages in each segment. The abdomen is made up of seven different sections.