The Collaborative International Dictionary of English v.0.48:

Lancelet \Lance"let\, n. [Lance + -let.] (Zool.)
   A small fishlike animal (Amphioxus lanceolatus), remarkable
   for the rudimentary condition of its organs. It is the type
   of the class Leptocardia. See Amphioxus, Leptocardia.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Amphioxus \Am`phi*ox"us\, n. [NL., fr. Gr. 'amfi` + ? sharp.]
   (Zool.)
   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.
   [1913 Webster]