Nephrozoa is a proposed major clade of bilateriananimals. It includes all bilaterians other than Xenacoelomorpha. It contrasts with the Xenambulacraria hypothesis, which instead posits that Xenacoelomorpha is most closely related to Ambulacraria.[1][2][3][4][5] Which hypothesis is correct is controversial. Authors supporting the Xenambulacraria hypothesis have suggested that the genetic evidence used to support Nephrozoa may be due to systematic error.[1]
Jondelius, Ulf; Ruiz-Trillo, Inaki; Baguna, Jaume; Riutort, Marta (April 2002). "The Nemertodermatida are basal bilaterians and not members of the Platyhelminthes". Zoologica Scripta. 31 (2): 201–215. doi:10.1046/j.1463-6409.2002.00090.x. ISSN0300-3256. S2CID84015834.