Cephalochordata
Encyclopedia
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 lancelet
s (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.. 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 . They have numerous gill slits, and have separate sexes. A well known example is the lancelet
.
Chordate
Chordates are animals which are either vertebrates or one of several closely related invertebrates. They are united by having, for at least some period of their life cycle, a notochord, a hollow dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail...
subphylum
Subphylum
In life, a subphylum is a taxonomic rank intermediate between phylum and superclass. The rank of subdivision in plants and fungi is equivalent to subphylum.Not all phyla are divided into subphyla...
defined by the presence of a notochord
Notochord
The notochord is a flexible, rod-shaped body found in embryos of all chordates. It is composed of cells derived from the mesoderm and defines the primitive axis of the embryo. In some chordates, it persists throughout life as the main axial support of the body, while in most vertebrates it becomes...
that persists throughout life. It is represented in the modern oceans by the lancelet
Lancelet
The lancelets , also known as amphioxus, are the modern representatives of the subphylum Cephalochordata, formerly thought to be the sister group of the craniates. They are usually found buried in sand in shallow parts of temperate or tropical seas. In Asia, they are harvested commercially as food...
s (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.. 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
Burgess Shale
The Burgess Shale Formation, located in the Canadian Rockies of British Columbia, is one of the world's most celebrated fossil fields, and the best of its kind. It is famous for the exceptional preservation of the soft parts of its fossils...
of British Columbia, which has yielded Pikaia
Pikaia
Pikaia gracilens is an extinct animal known from the Middle Cambrian Burgess Shale of British Columbia. -Discovery:It was discovered by Charles Walcott and was first described by him in 1911. It was named after Pika Peak, a mountain in Alberta, Canada. Based on the obvious and regular segmentation...
fossils. Recently a different cephalochordate fossil (Yunnanozoon
Yunnanozoon
Yunnanozoon lividum is a suspected a hemichordate or chordate from the Lower Cambrian, Chengjiang biota of Yunnan province, China....
) has been found in south China. It dates to the early Cambrian period and is the earliest known fossil of the cephalochordate lineage . They have numerous gill slits, and have separate sexes. A well known example is the lancelet
Lancelet
The lancelets , also known as amphioxus, are the modern representatives of the subphylum Cephalochordata, formerly thought to be the sister group of the craniates. They are usually found buried in sand in shallow parts of temperate or tropical seas. In Asia, they are harvested commercially as food...
.