Source : Webster's Revised Unabridged Dictionary (1913)

Amphioxus \Am`phi*ox"us\, n. [NL., fr. Gr. ? + ? sharp.]
   (Zo["o]l.)
   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, vertebr[ae], nor red blood. It forms
   the type of the group {Acrania}, {Leptocardia}, etc.

Source : WordNet®

amphioxus
     n : small translucent lancet-shaped burrowing marine animal;
         primitive forerunner of the vertebrates [syn: {lancelet}]
     [also: {amphioxi} (pl)]