Which phylum is most closely related to chordates?

Which phylum is most closely related to chordates?

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

Answer: (B)

The main idea is how animal groups are related by their early development. Chordates and echinoderms are both deuterostomes, meaning in their embryonic development the blastopore becomes the anus and the mouth forms later. This shared developmental pattern points to a closer common ancestor between chordates and echinoderms than with the other listed phyla. Among the choices, echinoderms are the closest relatives to chordates because mollusks and arthropods are protostomes (mouth forms first), and cnidarians are not even bilaterally symmetric and belong to a different branch of animals. So the deuterostome relationship links chordates more closely with echinoderms.

The main idea is how animal groups are related by their early development. Chordates and echinoderms are both deuterostomes, meaning in their embryonic development the blastopore becomes the anus and the mouth forms later. This shared developmental pattern points to a closer common ancestor between chordates and echinoderms than with the other listed phyla.

Among the choices, echinoderms are the closest relatives to chordates because mollusks and arthropods are protostomes (mouth forms first), and cnidarians are not even bilaterally symmetric and belong to a different branch of animals. So the deuterostome relationship links chordates more closely with echinoderms.