Both lancelets and tunicates belong to which phylum?

Both lancelets and tunicates belong to which phylum?

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

Answer: (B)

Chordates share a set of features that appear at some point in their development: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail. Lancelets retain all these features throughout their life, so they clearly fit in this phylum. Tunicates look very different as adults, but their larval stage shows the hallmark traits—such as the dorsal nerve cord and notochord—before they metamorphose. That common developmental plan places both groups inChordata, the same phylum that includes vertebrates. The other options describe groups with different body plans and features (for example, echinoderms with radial symmetry and water vascular systems, arthropods with segmented bodies and exoskeletons, mollusks with a muscular foot and mantle), which don’t share the defining chordate characteristics.

Chordates share a set of features that appear at some point in their development: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail. Lancelets retain all these features throughout their life, so they clearly fit in this phylum. Tunicates look very different as adults, but their larval stage shows the hallmark traits—such as the dorsal nerve cord and notochord—before they metamorphose. That common developmental plan places both groups inChordata, the same phylum that includes vertebrates. The other options describe groups with different body plans and features (for example, echinoderms with radial symmetry and water vascular systems, arthropods with segmented bodies and exoskeletons, mollusks with a muscular foot and mantle), which don’t share the defining chordate characteristics.