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Cephalozoa are an extinct class of primitive segmented marine organisms within the
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 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
*''
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 Nomenclatu ...
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 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 s ...
in the Arkhangelsk
Arkhangelsk (, ; rus, Арха́нгельск, p=ɐrˈxanɡʲɪlʲsk), also known in English as Archangel and Archangelsk, is a city and the administrative center of Arkhangelsk Oblast, Russia. It lies on both banks of the Northern Dvina near i ...
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 t ...
, approximately 635 to 540 Ma (millions of years ago).
Taxonomy
Cephalozoa includes the families Yorgiidae and Sprigginidae: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'' 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'' 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 fossi ...
'' Glaessner, 1958
**† '' Spriggina floundersi'' Glaessner, 1958
**† ''Spriggina ovata
''Marywadea'' is a genus of Ediacaran biota shaped like an oval with a central ridge. It is a bilaterian organism as evidenced by its symmetry, vaguely resembling a very primitive trilobite. The fossil has an asymmetrical first chamber of the qui ...
'' Glaessner and Wade, 1966 now considered synonym of ''Marywadea ovata''.
*† '' Marywadea'' Glaessner, 1976
**† ''Marywadea ovata
''Marywadea'' is a genus of Ediacaran biota shaped like an oval with a central ridge. It is a bilaterian organism as evidenced by its symmetry, vaguely resembling a very primitive trilobite. The fossil has an asymmetrical first chamber of the q ...
'' Glaessner and Wade, 1966
*† '' Cyanorus'' Ivantsov, 2004
**† ''Cyanorus singularis
''Cyanorus singularis'' is a small proarticulatan, closely related to ''Spriggina'' and ''Marywadea''. Its two largest pairs of appendages are located on the anterior part of the body. The anterior part of the body was most likely not segmented. ...
'' Ivantsov, 2004
*† '' Praecambridium'' Glaessner and Wade, 1966, previously classified as Yorgiidae; now considered a juvenile form of ''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 fossi ...
''
**† '' Praecambridium sigillum'' 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 ...
'' sometimes includes Cephalozoa:
*''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 ...
'' Fedonkin, 2002
**'' Andiva ivantsovi'' Fedonkin, 2002
Recent studies indicate that the family Yorgiidae 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 wit ...
.
See also
*Ediacaran fauna
The Ediacaran (; formerly Vendian) biota is a taxonomic period classification that consists of all life forms that were present on Earth during the Ediacaran Period (). These were composed of enigmatic tubular and frond-shaped, mostly sessi ...
References
Cephalozoa Ediacaran life {{Ediacaran-stub