Cephalozoa are an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differentl ...

of primitive segmented marine organisms within the

Phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature f ...

Proarticulata Proarticulata is a proposed phylum of extinct, bilaterally symmetrical animals known from fossils found in the Ediacaran (Vendian) marine deposits, and dates to approximately . The name comes from the Greek () = "before" and Articulata, i.e. pr ...

from the Ediacaran period. They possessed bilateral symmetry and were characterized by a thin, rounded body.

Description

Unlike the other classes of proarticulates, the segmentation of the body is not complete and shows a "head" with fine distribution channels. Some species of the

Yorgiidae Yorgiidae is an extinct family of cephalozoans, which lived 635 million years ago. They were filter fed. Description Like most proarticulates, they present semi-bilateral symmetry. They had a discoid appearance, with the body segmented by isome ...

family also show some asymmetry.Ivantsov, A. Y. (2004
"Vendian Animals in the Phylum Proarticulata"
The Rise and Fall of the Vendian Biota. IGSP Project 493. Abstracts. Prato, Italy, . They were discovered in Russia near the

White Sea The White Sea (russian: Белое море, ''Béloye móre''; Karelian and fi, Vienanmeri, lit. Dvina Sea; yrk, Сэрако ямʼ, ''Serako yam'') is a southern inlet of the Barents Sea located on the northwest coast of Russia. It is su ...

in the

Arkhangelsk Arkhangelsk (, ; rus, Арха́нгельск, p=ɐrˈxanɡʲɪlʲsk), also known in English as Archangel and Archangelsk, is a types of inhabited localities in Russia, city and the administrative center of Arkhangelsk Oblast, Russia. It lies o ...

region, where they lived during the

Ediacaran The Ediacaran Period ( ) is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and th ...

, approximately 635 to 540 Ma (millions of years ago).

Taxonomy

Cephalozoa includes the families

and

Sprigginidae Sprigginidae is an extinct family of cephalozoans characterized by having a greater number of isomers than its sister taxon, Yorgiidae. They lived approximately 635 million years ago, in the Ediacaran period. Distribution Fossils are found wit ...

Yorgiidae

*† ''

Archaeaspinus ''Archaeaspinus fedonkini'' is an extinct proarticulatan organism from the Late Precambrian (Ediacaran) period. Background ''Archaeaspinus'' was discovered in Zimnii Bereg, the Winter Coast of the White Sea in Russia, by A. Yu. Ivantsov in 2001 ...

'' Ivantsov, 2007 (synonym of ''Archaeaspis'') **† ''

Archaeaspinus fedonkini ''Archaeaspinus fedonkini'' is an extinct proarticulatan organism from the Late Precambrian ( Ediacaran) period. Background ''Archaeaspinus'' was discovered in Zimnii Bereg, the Winter Coast of the White Sea in Russia, by A. Yu. Ivantsov in 20 ...

'' Ivantsov, 2001 *† ''

Yorgia ''Yorgia waggoneri'' is a discoid Ediacaran organism. It has a low, segmented body consisting of a short wide "head", no appendages, and a long body region, reaching a maximum length of . It is classified within the extinct animal phylum Proarti ...

'' Ivantsov, 1999 **† ''

Yorgia waggoneri ''Yorgia waggoneri'' is a discoid Ediacaran organism. It has a low, segmented body consisting of a short wide "head", no appendages, and a long body region, reaching a maximum length of . It is classified within the extinct animal phylum Proart ...

'' Ivantsov, 1999

Sprigginidae

*† ''

Spriggina ''Spriggina'' is a genus of early bilaterian animals whose relationship to living animals is unclear. Fossils of ''Spriggina'' are known from the late Ediacaran period in what is now South Australia. ''Spriggina floundersi'' is the official fo ...

'' Glaessner, 1958 **† ''

Spriggina floundersi ''Spriggina'' is a genus of early bilaterian animals whose relationship to living animals is unclear. Fossils of ''Spriggina'' are known from the late Ediacaran period in what is now South Australia. ''Spriggina floundersi'' is the official fossi ...

'' Glaessner, 1958 **† '' Spriggina ovata'' Glaessner and Wade, 1966 now considered synonym of ''Marywadea ovata''. *† '' Marywadea'' Glaessner, 1976 **† '' Marywadea ovata'' Glaessner and Wade, 1966 *† '' Cyanorus'' Ivantsov, 2004 **† '' Cyanorus singularis'' Ivantsov, 2004 *† ''

Praecambridium ''Praecambridium sigillum'' is an extinct organism that superficially resembles a segmented trilobite-like arthropod. It was originally described as being a trilobite-like arthropod, though the majority of experts now place it within the Proartic ...

'' Glaessner and Wade, 1966, previously classified as Yorgiidae; now considered a juvenile form of ''

'' **† ''

Praecambridium sigillum ''Praecambridium sigillum'' is an extinct organism that superficially resembles a segmented trilobite-like arthropod. It was originally described as being a trilobite-like arthropod, though the majority of experts now place it within the Proartic ...

'' Glaessner and Wade, 1966 The genus ''

Andiva ''Andiva ivantsovi'' is a Vendian fossil, identified to be a bilaterian triploblastic animal in the Ediacaran phylum Proarticulata, known from the Winter Coast, White Sea, Russia. It was first discovered in 1977, and described as a new species i ...

'' sometimes includes Cephalozoa:

*''

'' Fedonkin, 2002 **''

Andiva ivantsovi ''Andiva ivantsovi'' is a Vendian fossil, identified to be a bilaterian triploblastic animal in the Ediacaran phylum Proarticulata, known from the Winter Coast, White Sea, Russia. It was first discovered in 1977, and described as a new spe ...

'' Fedonkin, 2002 Recent studies indicate that the family

could be included or closely related to the class

Vendiamorpha Vendiamorpha is a class of extinct animals within the Ediacaran phylum Proarticulata. The typical vendiamorph had an oval-shaped or round-shaped body divided completely into segmented isomers, that were arranged alternately in two rows with ...

References

Cephalozoa Ediacaran life {{Ediacaran-stub

Description

Taxonomy

Yorgiidae

Sprigginidae

See also

References