Cephalaspidomorphs are a taxon of jawless fishes named for the cephalaspids, which is another name for the osteostracans. Most of the members of this group are extinct; however, it interests modern biologists because it may include the lampreys. If so, the lampreys extend the known range of the group from the Silurian and Devonian periods to the present day. Scientific classification or biological classification is how biologists group and categorize extinct and living species of organisms (as opposed to folk taxonomy). ... Phyla Subregnum Parazoa Porifera (sponges) Subregnum Agnotozoa Placozoa (trichoplax) Orthonectida (orthonectids) Rhombozoa (rhombozoans) Subregnum Eumetazoa Radiata (unranked) (radial symmetry) Ctenophora (comb jellies) Cnidaria (coral, jellyfish, anemones) Bilateria (unranked) (bilateral symmetry) Acoelomorpha (basal) Orthonectida (parasitic to 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... Vertebrata is a subphylum of chordates, specifically, those with backbones or spinal columns. ... Osteostraci (Cephalaspidiformes) are an extinct marine subgroup of the agnatha. ... Galeaspida (galeaspids) are an extinct taxon of jawless marine fish and a subgroup of the Cephalaspidomorphi, which are itself a subgroup of the vertebrate. ... Pituriaspida are an extinct taxon of jawless marine fish and a subgroup of the Cephalaspidomorphi, which are itself a subgroup of the vertebrate. ... Anaspida are a extinct marine subgroup of the agnatha. ... Subfamilies Geotriinae Mordaciinae Petromyzontinae A lamprey is a jawless fish with a toothed, funnel-like sucking mouth, with which most species bore into the flesh of other fishes to suck their blood. ... A taxon (plural taxa), or taxonomic unit, is a grouping of organisms (named or unnamed). ... Groups Myxini(hagfish) Hyperoartia Petromyzontidae(lampreys) Pteraspidomorphi Thelodonti Anaspida Cephalaspidomorphi Galeaspida Pituriaspida Osteostraci Agnatha (Greek, no jaws) is a Ġ ġ İ ı Ż ż paraphyletic superclass of jawless fish in the phylum Chordata, subphylum Vertebrata. ... Osteostraci (Cephalaspidiformes) are an extinct marine subgroup of the agnatha. ... Subfamilies Geotriinae Mordaciinae Petromyzontinae A lamprey is a jawless fish with a toothed, funnel-like sucking mouth, with which most species bore into the flesh of other fishes to suck their blood. ... The Silurian is a major division of the geologic timescale that extends from the end of the Ordovician period, about 443. ... == == Disambiguation: Devonian is sometimes used to refer to the Southwestern Brythonic language, and the people of the county of Devon are sometimes referred to as Devonians The Devonian is a geologic period of the Paleozoic era. ...

Classification

In the 1920s, the biologists Kiaer and Stensiö first recognized the Cephalaspidomorphi as including the osteostracans, anaspids, and lampreys, because all three groups share a single dorsal "nostril", now known as a nasohypophysial opening. Anaspida are an extinct marine subgroup of the agnatha. ...

Since then, opinions on the relations among jawless vertebrates have varied. Most workers have come to regard the agnatha as paraphyletic, having given rise to the jawed fishes. Because of shared features such as paired fins, the origins of the vertebrates may lie within the Cephalaspidomorphi. Some biologists no longer use the name Cephalaspidomorphi because relations among osteostraci and anaspida are unclear, and the affinities of the lampreys are also contested. Others have restricted the cephalaspidomorphs to include only groups more clearly related to the Osteostraci, such as Galeaspida and Pituriaspida, that were largely unknown in the 1920s. Groups Myxini(hagfish) Hyperoartia Petromyzontidae(lampreys) Pteraspidomorphi Thelodonti Anaspida Cephalaspidomorphi Galeaspida Pituriaspida Osteostraci Agnatha (Greek, no jaws) is a Ġ ġ İ ı Ż ż paraphyletic superclass of jawless fish in the phylum Chordata, subphylum Vertebrata. ... Paraphyletic - Wikipedia /**/ @import /skins-1. ... For the echinoderm, see Gnathostomata (echinoid) Classes Placodermi Chondrichthyes Acanthodii Osteichthyes Gnathostomata is the group of vertebrates with jaws. ... Galeaspida (galeaspids) are an extinct taxon of jawless marine fish and a subgroup of the Cephalaspidomorphi, which are itself a subgroup of the vertebrate. ... Pituriaspida are an extinct taxon of jawless marine fish and a subgroup of the Cephalaspidomorphi, which are itself a subgroup of the vertebrate. ...

Lampreys

Many reference works still regard Cephalaspidomorphi as a Linnean class whose sole living representaties are the lampreys. Linnaean taxonomy classifies living things into a hierarchy, originally starting with kingdoms. ... Scientific classification or biological classification refers to how biologists group and categorize extinct and living species of organisms. ... Subfamilies Geotriinae Mordaciinae Petromyzontinae A lamprey is a jawless fish with a toothed, funnel-like sucking mouth, with which most species bore into the flesh of other fishes to suck their blood. ...

External Links

• The Tree of Life discusses relations among jawless fish
• Palaeos site regarding Cephalaspidomorphi

References

Stensiö, E. A. (1927). The Devonian and Downtonian vertebrates of Spitsbergen. 1. Family Cephalaspidae. Skrifter om Svalbard og Ishavet, 12, 1-391.