What distinguishes chordates from other phyla?

Chordates are distinguished from other animal phyla primarily by the presence of a notochord, which is a flexible, rod-like structure that provides support and is a key feature during the embryonic stage of development. This notochord is crucial as it serves as the precursor to the vertebral column (spine) in vertebrates, providing a scaffold for the development of the nervous system and other structures.

While bilateral symmetry is a characteristic shared by many animals, including some non-chordates, it is not unique to chordates. Similarly, the assertion that chordates are warm-blooded is not accurate, as not all chordates, such as reptiles and fish, maintain a warm-blooded metabolism. The presence of limbs is also not exclusive to chordates, as these structures can be found in various forms across several other animal groups, including arthropods and some mollusks.

Thus, the defining feature of chordates that sets them apart from other phyla is the notochord, marking their unique evolutionary lineage within the kingdom Animalia.