You behold a creature very similar to your own ancient, tiny ancestor
A note for The Half-Lesson, "Your Brain Is Not for Thinking," in Seven and a Half Lessons About the Brain by Lisa Feldman Barrett.
Some context from page 2 is:
When you look at a modern amphioxus, you behold a creature very similar to your own ancient, tiny ancestor who roamed the same seas.
Scientists believe that our common ancestor with amphioxi resembled modern amphioxi very closely.
For many years, scientists believed that the common ancestor of amphioxus and vertebrates was an extinct, amphioxus-looking animal called Pikaia. Some scientists now suggest that another fossil animal, Cathaymyrus, might be closer to a vertebrate than an amphioxus.[1]
For more information amphioxus evolution and the debates therein, see these references.[1][2]