Pikaia
Pikaia is an extinct animal known from the Middle Cambrian fossil found near Mount Pika in the Burgess Shale of British Columbia. It was discovered by Charles Walcott and was first described by him in 1911. Based on the obvious and regular segmentation of the body, Walcott classified it as a Polychaete worm. It resembles a living chordate commonly known as the lancelet.
During his re-examination of the Burgess Shale fauna in 1979, Paleontologist Conway Morris placed Pikaia gracilens in the chordates, making it perhaps the oldest known ancestor of modern vertebrates.
Averaging about 40mm in length, Pikaia swam above the seafloor using its body and an expanded tail fin. Pikaia may have filtered particles from the water as it swam along. Only 60 specimens have been found to date.