Lancelets are usually about 1 in. There is no distinct head and no paired fins. Small food particles enter the pharynx through the mouth and are filtered out as the water exits through the gill slits.
Respiration probably occurs mostly through the skin.
The lancelet has a dorsal notochord, or stiffening rod, extending from tip to tail, that gives it its characteristic pointed shape. In the lancelet there is a nerve cord above the notochord, but no brain and no eyes. It is thought that vertebrates evolved from ancestors similar to lancelets. The larva of the lamprey , the most primitive living vertebrate, resembles a lancelet in many respects. Lancelets are classified in the phylum Chordata , subphylum Cephalochordata.