Category:Nephrozoa

Nephrozoa is a major clade of bilaterians, divided into the protostomes and the deuterostomes, containing almost all animal phyla and over a million extant species. Its sister clade is the Xenacoelomorpha. The Ambulacraria (conventionally deuterostomes) may actually be sister to the Xenacoelomorpha, forming the Xenambulacraria as basal Deuterostomes, or basal Bilateria invalidating Nephrozoa and Deuterostomes.[1][2] The coelom, the excretory organs, and nerve cords developed in the Nephrozoa.[3] Chordates (which include all the vertebrates) are deuterostomes.[4] It seems very likely that the 555 million year old Kimberella was a member of the protostomes.[5][6] 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.[4]