Concept:
Phylum Chordata is defined by a distinct suite of fundamental morphological traits present at some stage of their development. Identifying non-chordate properties requires evaluating these key distinguishing markers against non-chordate invertebrates.
Step 1: Review the core characteristics of Chordates
True chordates are uniquely distinguished by four diagnostic features:
• Notochord: A solid, flexible, rod-like skeletal structure running along the dorsal side during embryonic development.
• Dorsal Hollow Nerve Cord: A single central nervous system strand located dorsally relative to the digestive tract.
• Pharyngeal Gill Slits: Pairs of lateral openings or clefts in the wall of the pharynx, which function in respiration or filter feeding (retained as gills in fish or modified into alternative structures in higher terrestrial vertebrates during embryonic development).
• Post-anal Tail: An elongation of the body extending past the anus.
Step 2: Evaluate the statement "Absence of gills"
Since
pharyngeal gill slits are a defining baseline characteristic of chordates, stating that chordates are characterized by an absence of gills is factually incorrect. Many aquatic chordates (like fishes and protochordates) actively maintain functioning gills throughout their lives.
Because the question explicitly asks for the feature that is
NOT a characteristic of chordates, option (4) is the correct choice.
