Discovery of a single specimen of a shrimp fossil from the Devonian Woodford Shale in the Ryan Quarry, near Ada, Oklahoma, documents the oldest occurrence of a penaeoid decapod crustacean, Aciculopoda mapesi n. gen., n. sp. within the Aciculopodidae n. fam. The specimen lacks any diagnostic features of the primitive Paleozoic eumalacostracans, including caudal furca, but possesses the characteristic form and preservational style of the Superorder Eucarida, particularly the Superfamily Penaeoidea. The shrimp specimen is remarkably preserved; it has been phosphatized, and the muscles of the pleon have been preserved completely enough that discrete muscle bands are discernable. The cuticle of the cephalothorax is shattered into small fragments, whereas that of the pleon is absent except for the telson. Confirmation that this specimen represents a Devonian decapod documents only the second decapod taxon known from the Devonian and the third from the Paleozoic. It is the earliest known shrimp and one of the two oldest decapods, both from North America.