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
Superphylum Deuterostomia Chordata Hemichordata Echinodermata 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 Chaetognatha
Synonyms
Eubilateria Peter Ax, 1987

Eubilateria Peter Ax, 1987

Nephrozoa is a clade of basal bilaterians in which the deuterostomes, and protostomes (incl. the basal arrow worms) emerged as sister clade of the Xenacoelomorpha.

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.