| Cephalochordata | |
|---|---|
| A Branchiostoma lanceolatum lancelet | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Subphylum: | Cephalochordata Owen, 1846 |
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 lancelets (also known as Amphioxus). The characteristics of Cephalochordata are that 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.[1]. The members of this phylum are very small and have no hard parts, making their fossils difficult to find. Fossilized species have been found in very old rocks predating vertebrates. There is famous shale fossil from the Middle Cambrian Burgess Shale of British Columbia, which has yielded Pikaia fossils. Recently a different cephalochordate fossil (Yunnanozoon) has been found in south China. It dates to the early Cambrian period and is the earliest known fossil of the cephalochordate lineage [2]. They have numerous gill slits, and have separate sexes. A well known example is the lancelet.