Cephalochordata (from Greek: κεφαλή kephalé, "head" and χορδή khordé, "chord") is a chordate subphylum defined by the presence of a notochord that persists throughout life. It is represented in the modern oceans by the Amphioxiformes (lancelets, also known as amphioxus). Along with its sister phylum Urochordata, Cephalochordata can be classified as belonging to the taxon Protochordata.