Cephalochordata
Cephalochordata is a chordate subphylum defined by the presence of a notochord that persists throughout life. It is represented in the modern oceans by the lancelets. they are marine animals, segmented, and that they possess elongated bodies with a notochord that extends the length of the body and cirri surrounding the mouth for obtaining food.In cephalochordata the notochord extends from head to tail and it persists throughout their life. The members of this subphylum are very small and have no hard parts, making their fossils difficult to find.