exopods

Exopod is the outer branch of a biramous limb in arthropods. It arises from the proximal base of the limb, the protopod, and is distinct from the endopod, the inner branch. In many crustaceans and some extinct arthropods, limbs are biramous and consist of an endopod and an exopod that may differ in size and articulation with the limb base. The exopod is typically the more lateral branch and can be segmented; it often bears setae or blade-like paddles and may carry gill filaments (epipod) in some groups. Functionally, exopods contribute to locomotion, respiration, feeding, or a combination of roles, depending on the taxon.

In living crustaceans, exopods may form swimming appendages, such as the outer branch of thoracic or pleopodal limbs, or serve sensory or manipulative tasks. In many fossil arthropods, including trilobites, exopods appear as lateral lobes of the limbs, sometimes broad and paddle-like, indicating an important role in swimming and/or respiration.

The term exopod is used primarily in the study of crustacean and arthropod limb morphology. Not all arthropods have biramous limbs; most hexapods (insects) and many chelicerates lack an exopod, reflecting their uniramous limb organization.