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Temporal range: Ediacaran - Present, 555–0 Ma
An arrow worm, Spadella cephaloptera
Scientific classification e
Kingdom: Animalia
Clade: Bilateria
Clade: Nephrozoa
Jondelius et al. , 2002

Eubilateria Peter Ax, 1987

Nephrozoa is a clade of bilaterians which includes arrow worms, deuterostomes, and protostomes. It is a sister clade to the Xenacoelomorpha, with which it forms the Bilateria clade.

The majority of animals more complex than jellyfish and other Cnidarians are split into two groups, the protostomes and deuterostomes. Chordates (which include all the vertebrates) are deuterostomes.[1] It seems very likely that the 555 million year old Kimberella was a member of the protostomes.[2][3] If so, this means that the protostome and deuterostome lineages must have split some time before Kimberella appeared — at least 558 million years ago, and hence well before the start of the Cambrian 541 million years ago.[1]


  1. ^ a b Erwin, Douglas H.; Eric H. Davidson (1 July 2002). "The last common bilaterian ancestor". Development. 129 (13): 3021–3032. PMID 12070079. 
  2. ^ New data on Kimberella, the Vendian mollusc-like organism (White sea region, Russia): palaeoecological and evolutionary implications (2007), "Fedonkin, M.A.; Simonetta, A; Ivantsov, A.Y.", in Vickers-Rich, Patricia; Komarower, Patricia, The Rise and Fall of the Ediacaran Biota, Special publications, 286, London: Geological Society, pp. 157–179, doi:10.1144/SP286.12, ISBN 9781862392335, OCLC 156823511 
  3. ^ Butterfield, N.J. (December 2006). "Hooking some stem-group "worms": fossil lophotrochozoans in the Burgess Shale". BioEssays. 28 (12): 1161–6. doi:10.1002/bies.20507. PMID 17120226.