Which phylum includes all animals with a dorsal nerve cord?

Which phylum includes all animals with a dorsal nerve cord?

• A. Chordata
• B. Echinodermata
• C. Porifera
• D. Arthropoda

Answer: (A)

Having a dorsal nerve cord is the defining feature of chordates. In chordates, this hollow nerve cord runs along the back and, in vertebrates, develops into the brain and spinal cord. Other groups don’t share this trait: echinoderms rely on a nerve ring and branching nerves rather than a dorsal cord; poriferans lack a true nervous system; arthropods have a ventral nerve cord with segmental ganglia. Because the dorsal nerve cord uniquely characterizes chordates, this phylum includes all animals with that feature, including the various invertebrate chordates where the nerve cord is present at least at some life stage.

Having a dorsal nerve cord is the defining feature of chordates. In chordates, this hollow nerve cord runs along the back and, in vertebrates, develops into the brain and spinal cord. Other groups don’t share this trait: echinoderms rely on a nerve ring and branching nerves rather than a dorsal cord; poriferans lack a true nervous system; arthropods have a ventral nerve cord with segmental ganglia. Because the dorsal nerve cord uniquely characterizes chordates, this phylum includes all animals with that feature, including the various invertebrate chordates where the nerve cord is present at least at some life stage.