Jeffrey H. Schwartz Quote

If Walter Garstang's suggestion is correct, and chordates did arise from a tunicate-like form by retaining the chordate features of their larval stage of development into adulthood, then the first chordates must have been affected by a regulatory mutation that kept the Manx gene activated for a longer period of time.

Sudden Origins: Fossils, Genes, and the Emergence of Species (1999)