Cephalozoa

Cephalozoa are an extinct class of primitive segmented marine organisms within the Phylum Proarticulata 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.
They were discovered in Russia near the White Sea in the Arkhangelsk region, where they lived during the Ediacaran, approximately 635 to 540 Ma.

Cephalozoa includes the families Yorgiidae and Sprigginidae, as well as genera not assigned to any family:

† Archaeaspinus Ivantsov, 2007
*† Archaeaspinus fedonkini Ivantsov, 2001
† Yorgia Ivantsov, 1999
*† Yorgia waggoneri Ivantsov, 1999
Sprigginidae
† Spriggina Glaessner, 1958
*† Spriggina floundersi 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 Glaessner and Wade, 1966, previously classified as Yorgiidae; now considered a juvenile form of Spriggina
*† Praecambridium sigillum Glaessner and Wade, 1966

The genera Cephalonega,''Andiva, Lossinia, Ivovicia and Podolimirus are also included in Cephalozoa, although are not part of any family:

Recent studies indicate that the family Yorgiidae could be included or closely related to the class Vendiamorpha.