How does the position of a chordate nerve cord differ from that of nerve cords in most other animal phyla?

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A translucent X-ray fish (Pristella maxillaris) swims in an aquarium, showing its visible backbone and internal structures through its body. — Chordate X-ray fish (*Pristella maxillaris*), is an example of a chordate with a visible backbone.

In chordates, the nerve cord is positioned dorsally—meaning it is located above the gut and the notochord. This tubular, dorsal arrangement is a defining characteristic of the phylum Chordata.1234

In contrast, most other animal phyla (such as many elongated invertebrates like earthworms) typically possess a ventral nerve cord, which is located below the gut. Additionally, while the chordate nerve cord is characteristically hollow, the nerve cords found in many other invertebrate groups are often solid.32