Nephrozoa

Nephrozoa Temporal range: Ediacaran - Present, 555–0 Ma PreЄ Є O S D C P T J K Pg N
An arrow worm, Spadella cephaloptera
Scientific classification
Kingdom:	Animalia
Clade:	Bilateria
Clade:	Nephrozoa Jondelius et al. , 2002
Phyla
Chaetognatha Superphylum Deuterostomia Chordata Hemichordata Echinodermata Xenacoelomorpha Vetulicolia † Protostomia (unranked) Superphylum Ecdysozoa Kinorhyncha Loricifera Priapulida Nematoda Nematomorpha Onychophora Tardigrada Arthropoda Superphylum Platyzoa Platyhelminthes Gastrotricha Rotifera Acanthocephala Gnathostomulida Micrognathozoa Cycliophora Superphylum Lophotrochozoa Sipuncula Hyolitha † Nemertea Phoronida Bryozoa Entoprocta Brachiopoda Mollusca Annelida
Synonyms
Eubilateria Peter Ax, 1987

Nephrozoa is a clade of bilaterians which includes arrow worms, deuterostomes, and protostomes.

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. It seems very likely that the 555 million year old Kimberella was a member of the protostomes. 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.

References

• Balavoine, G.; Adoutte, A. 1998: One or three Cambrian radiations? Science, 280: 397-398.
• Bourlat, S.J.; Nielsen, C.; Economou, A.D.; Telford, M.J. 2008: Testing the new animal phylogeny: a phylum level molecular analysis of the animal kingdom. Molecular phylogenetics and evolution, 49: 23-31.
• Jondelius, U.; Ruiz-Trillo, I.; Baguñà, J.; Riutort, M. 2002: The Nemertodermatida are basal bilaterians and not members of the Platyhelminthes. Zoologica scripta, 31: 201-215.