What is one characteristic that separates chordates from all other animals?

The defining characteristic that separates chordates from all other animals is the presence of a hollow dorsal nerve cord. This structure is part of the central nervous system in chordates, which includes not only vertebrates but also some invertebrate groups like tunicates and lancelets. During embryonic development, this nerve cord forms from the ectoderm and plays a crucial role in the formation of the brain and spinal cord.

The presence of a hollow dorsal nerve cord is significant because it reflects a level of complexity in the nervous system that is not found in other animal phyla. While true coelom and bilateral symmetry are features seen in many animal groups, and the blastopore's fate varies across the animal kingdom, the hollow dorsal nerve cord is unique to chordates, marking a key evolutionary advancement. This characteristic demonstrates how chordates have developed a more sophisticated approach to neural organization compared to other animal lineages.