What specific structural feature is shared among all members of Phylum Chordata, including the sapsucker?
The presence of a notochord, dorsal hollow nerve cord, pharyngeal slits, or post-anal tail at some life cycle stage
The designation into Phylum Chordata (or subphylum Craniata) is based on a fundamental set of characteristics present at least transiently during the organism's development. These defining structures include the notochord, which provides flexible structural support; a dorsal hollow nerve cord, which develops into the central nervous system; pharyngeal slits; and a post-anal tail. For the adult Yellow-bellied Sapsucker, this blueprint manifests clearly in its internal skeletal structure, namely its vertebral column or backbone. This shared structural heritage firmly places it within the broad group encompassing mammals, fish, and reptiles, linking its axial support system to that of these diverse creatures.
