Which of the following is NOT a diagnostic feature of the phylum Chordata?

• A. Exoskeleton made of chitin
• B. Dorsal hollow nerve cord
• C. Presence of a notochord
• D. Pharyngeal gill slits

Answer: (A)

Verified step by step guidance

1. Understand the diagnostic features of the phylum Chordata. Chordates are defined by specific characteristics that are present at some stage of their life cycle, including a dorsal hollow nerve cord, a notochord, and pharyngeal gill slits.
2. Review the feature 'Exoskeleton made of chitin.' Chitin is a structural polysaccharide commonly found in the exoskeletons of arthropods, not in chordates. Chordates typically have endoskeletons made of cartilage or bone.
3. Compare the feature 'Dorsal hollow nerve cord.' This is a key characteristic of chordates, forming the basis of the central nervous system (brain and spinal cord).
4. Examine the feature 'Presence of a notochord.' The notochord is a flexible, rod-like structure that provides support and is a defining trait of chordates, present at least during embryonic development.
5. Analyze the feature 'Pharyngeal gill slits.' These are openings in the pharynx that are present in chordates during some stage of their development, often associated with filter feeding or respiration.