What does amphioxus mean?
The definition of amphioxus
Am`phi*ox”us, n.
Etym: [NL., fr. Gr. (Zoöl.)

A fishlike creature (Amphioxus lanceolatus), two or three inches long, found in temperature seas; — also called the lancelet. Its body is pointed at both ends. It is the lowest and most generalized of the vertebrates, having neither brain, skull, vertebræ, nor red blood. It forms the type of the group Acrania, Leptocardia, etc.