The neurobiology of the ascidian tadpole larva: recent developments in an ancient chordate
These are candidates for genes specific to chordates
," says Rokhsar.
The new Chengjiang species have a number of features not seen in amphioxus or other invertebrate chordates
Before the discovery of Cathaymyrus, the oldest fossil generally recognized as a chordate
was the 520-million-year-old Pikaia from Canada's Burgess Shale fossil beds.
Whereas putative vertebrates appear in the late Cambrian, around 520 million years ago, their chordate
ancestors apparently reach back to the main burst of the evolutionary event known as the Cambrian explosion.
The history of a developmental stage: metamorphosis in chordates
Researchers said hemichorates also share many characteristics with chordates
- which are a group of animals that humans belong to.
Hundreds of thousands of fossils representing a myriad of species of soft-bodied algae, sponges, worms (annelids and priapulids), primitive arthropods (a group that today includes insects and shrimps), and primitive members of the group humans belong to, the chordates
, have been collected.
Carroll, "Homeotic Genes and the Evolution of Arthropods and Chordates
," Nature 376 (2005): 479-85.
Chapters on Simple Animals, Cnidarians, Flatworms and Roundworms, Segmented Worms, Mollusks, Arachnids, Crustaceans, Centipedes and Millipedes, Insects, Echinoderms, Chordates
, Cartilaginous Fish, Bony Fish, Amphibians, Reptiles, Birds and Mammals are included, along with a Glossary and index.
In addition, many students have never learned about the subphylum Urochordata (sea squirts/tunicates) and are under the mistaken impression that all chordates
have a back bone.
They also remain a neglected component relative to the far less diverse chordates
(64,788 species) and plants (297,857 species), with 75 %<> of the 18,000 new species described in 2007 being invertebrates and an estimated 5,396,465 invertebrate species still remaining to be described globally (Chapman 2009).