Any of numerous animals belonging to the phylum Chordata, having at some stage of development a dorsal nerve cord, a notochord, and gill slits and including all vertebrates and certain marine animals, such as the lancelets.

• 脊索动物包括所有的脊椎动物以及如文昌鱼之类的海洋动物的脊索动物门的大量动物中的任一个，在某些生长阶段有背部神经索、背索及鳃裂