Final answer:
Vertebrates are unique among chordates for having a hollow dorsal nerve cord, which becomes the central nervous system consisting of the brain and spinal cord. This is in contrast to invertebrates, which generally have a solid ventral nerve cord. Humans are chordates with a notochord during embryonic development, which is replaced by a vertebral column in adults.
Step-by-step explanation:
Vertebrates are distinguished by their hollow dorsal nerve cord, which is a feature unique to the subphylum and contributes to their advanced central nervous system (CNS). In contrast, invertebrates often have a solid ventral nerve cord. The dorsal hollow nerve cord is derived from the ectoderm during embryonic development and is located above the notochord in chordates. This nerve cord eventually develops into the brain and spinal cord, forming the complex CNS found in vertebrates, including humans. It's worth noting that humans are indeed chordates and posses a notochord during embryonic development, and that vertebrates do have a notochord at some stage, which is replaced by the vertebral column in adulthood.
Evolutionarily, it is theorized that the transition from the ventrally located solid nerve cord of invertebrates to the dorsally located hollow nerve cord in vertebrates indicates a major shift in body plan organization that accompanied the increasing complexity of animals with a backbone.