How do branchiopod limbs function in swimming and respiration?

The primitive branchiopod limb functions as a multipurpose flap that serves simultaneously for locomotion, feeding, and respiration.1

Swimming

In notostracans and anostracans, the trunk limbs beat in a rhythmic sequence, forcing jets of water sideways and backward from the spaces between the limbs to propel the animal forward. Some anostracans possess complex musculature and flap systems within these limbs, allowing them to modify their movements to hover in place. In contrast, other branchiopod orders primarily utilize their antennae for swimming rather than their trunk limbs.21

Respiration

The branchiopod limb facilitates respiration through its structure as a thin-walled, flaplike appendage. Because the exoskeleton of branchiopods is generally thin and flexible, these limbs allow for gas exchange across the body surface. In many crustaceans, respiration is further supported by specialized outgrowths of the appendages known as epipodites, which are thin-walled, lamellate structures that function as gills. These structures increase the surface area available for gas exchange, enabling the animal to extract oxygen from the surrounding water.134