Which phylum includes animals with a dorsal hollow nerve cord at some life stage?

Which phylum includes animals with a dorsal hollow nerve cord at some life stage?

• A. Cnidaria
• B. Chitin
• C. Crustacea
• D. Chordata

Answer: (D)

The main idea here is that having a dorsal hollow nerve cord is a defining feature of chordates. In chordates, this nerve cord runs along the back and forms during development, eventually becoming the central nervous system in most members. Importantly, this structure is present at least at some life stage, such as in embryonic development or larval forms of tunicates and cephalochordates. Other groups don’t have this feature: Cnidarians have a simple nerve net rather than a dorsal nerve cord; “Chitin” isn’t a phylum or a body-plan feature at all; crustaceans are arthropods with a ventral nerve cord, not a dorsal one. So the phylum that includes animals with a dorsal hollow nerve cord at some life stage is the group containing chordates.

The main idea here is that having a dorsal hollow nerve cord is a defining feature of chordates. In chordates, this nerve cord runs along the back and forms during development, eventually becoming the central nervous system in most members. Importantly, this structure is present at least at some life stage, such as in embryonic development or larval forms of tunicates and cephalochordates. Other groups don’t have this feature: Cnidarians have a simple nerve net rather than a dorsal nerve cord; “Chitin” isn’t a phylum or a body-plan feature at all; crustaceans are arthropods with a ventral nerve cord, not a dorsal one. So the phylum that includes animals with a dorsal hollow nerve cord at some life stage is the group containing chordates.