Illustration of a pikaia. It is a Burgess shale fossil cephalochordate which looked like a 5-10cms eel. The presence of myomeres and a chordate means that it is sometimes considered a precursor of the vertebrates. Nevertheless, its character as ancestor of the vertebrates is not universally recognised, due to the presence of small tentacles, which are unusual. The amphioxus, which lives now, ressembles a pikaia.