Hemichordata is a phylum of worm-shaped marine deuterostome animals, generally considered the sister group of our own, the chordates. They date back to the Lower or Middle Cambrian and include an important class of fossils called graptolites, most of which became extinct in the Carboniferous. They seem to have a primtive form of a chordata, but this is most likely the result of parallell evolution. A hollow neural tube among some species (at least in early life), a probably a primitive trait they share with the common ancestor of chordata and the rest of the deuterostomes. Scientific classification or biological classification is how biologists group and categorize extinct and living species of organisms. ... Phyla Porifera (sponges) Ctenophora (comb jellies) Cnidaria (coral, jellyfish, anenomes) Placozoa (trichoplax) Subregnum Bilateria (bilateral symmetry) Acoelomorpha (basal) Orthonectida (flatworms, echinoderms, etc. ... Phyla Radiata Cnidaria Ctenophora - Comb jellies Bilateria Protostomia Acoelomorpha Platyhelminthes - Flatworms Nemertina - Ribbon worms Gastrotricha Gnathostomulida - Jawed worms Micrognathozoa Rotifera - Rotifers Acanthocephala Priapulida Kinorhyncha Loricifera Entoprocta Nematoda - Roundworms Nematomorpha - Horsehair worms Cycliophora Mollusca - Mollusks Sipuncula - Peanut worms Annelida - Segmented worms Tardigrada - Water bears Onychophora - Velvet worms Arthropoda - Insects, etc. ... Illustration of the different types of symmetry of Life Forms On Earth. ... Phyla Chaetognatha Echinodermata Hemichordata Chordata Deuterostomes (from the Greek: second the mouth) are one of the two superphyla of animals in the taxonomic branch bilateria, the other being the protostomes. ... William Bateson (August 8, 1861—February 8, 1926) was a British geneticist. ... Families Harrimaniidae Protoglossidae Ptychoderidae Saxipendiidae Spengelidae Torquaratoridae The Acorn worms or Enteropneusta are a hemichordate class of invertebrates. ... Pterobranchia is a zoological group established by Ray Lankester in 1877. ... Phylum (plural: phyla) is a taxon used in the classification of animals, adopted from the Greek phylai the clan-based voting groups in Greek city-states. ... Phyla Echinodermata Hemichordata Chordata Chaetognatha Deuterostomes (taxonomic term: Deuterostomia; from the Greek: other mouth) are a superphylum of animals. ... Phyla Porifera (sponges) Ctenophora (comb jellies) Cnidaria (coral, jellyfish, anenomes) Placozoa (trichoplax) Subregnum Bilateria (bilateral symmetry) Acoelomorpha (basal) Orthonectida (flatworms, echinoderms, etc. ... Typical Classes Subphylum Urochordata - Tunicatas Ascidiacea Thaliacea Larvacea Subphylum Cephalochordata - Lancelets Subphylum Myxini - Hagfishes Subphylum Vertebrata - Vertebrates Petromyzontida - Lampreys Placodermi (extinct) Chondrichthyes - Cartilaginous fishes Acanthodii (extinct) Actinopterygii - Ray-finned fishes Actinistia - Coelacanths Dipnoi - Lungfishes Amphibia - Amphibians Reptilia - Reptiles Aves - Birds Mammalia - Mammals Chordates (phylum Chordata) include the vertebrates, together with... The Cambrian is a major division of the geologic timescale that begins about 542 Ma (million years ago) at the end of the Proterozoic eon and ended about 488. ... A fossil Ammonite Fossils (from Latin fossus, literally having been dug up) are the mineralized or otherwise preserved remains or traces (such as footprints) of animals, plants, and other organisms. ... Graptolites (Graptolithina) are colonial animals known chiefly from the Upper Cambrian through the Mississippian (Lower Carboniferous). ... The Carboniferous is a major division of the geologic timescale that extends from the end of the Devonian period, about 359. ...

Hemichordata are divided into two classes: the Enteropneusta, commonly called acorn worms, and the Pterobranchia, which may include the graptolites. The phylum contains about 100 living species. The exact taxonomic position of hemichordata and whether the group is monophyletic is currently under debate. Families Harrimaniidae Protoglossidae Ptychoderidae Saxipendiidae Spengelidae The Acorn worms or Enteropneusta are a hemichordate class of invertebrates. ... Pterobranchia is a zoological group established by Ray Lankester in 1877. ... In phylogenetics, a group is monophyletic (Greek: of one stem) if all organisms in that group are known to have developed from a common ancestral form, and all descendants of that form are included in the group. ...

References

• Cameron, C. B. Classification of the extant hemichordata
• At the Tree of Life