How is the complexity of the structure of chordates manifested in comparison with invertebrates, for example, annelids?

The complication of the structure of chordates in comparison with invertebrates is manifested in the fact that in chordates an internal skeleton appears (in lower-organized ones, for example, lancelet (noncranial) or ascidians (tunicates) – chord), a heart appears, the neural tube is displaced to the dorsal part of the body. In the higher chordates, the central nervous system is divided into the spinal cord and the brain.

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