The Spiralia are a morphologically diverse clade of protostome animals, including within their number the molluscs, annelids, platyhelminths and other taxa.

[4] The term Spiralia is applied to those phyla that exhibit canonical spiral cleavage, a pattern of early development found in most members of the Lophotrochozoa.

Other spiralian phyla (rotifers, brachiopods, phoronids, gastrotrichs, and bryozoans) are also said to display a derived form of spiral cleavage in at least a portion of their constituent species, although evidence for this is sparse.

[7] Evidence of a close relationship between molluscs, annelids and lophophorates was found in 1995 and Lophotrochozoa was defined as the group containing these taxa and all the descendants of their last common ancestor.

[23] Ecdysozoa Mollusca Nemertea Annelida Brachiopoda Phoronida Bryozoa Entoprocta Cycliophora Gastrotricha Gnathifera Platyhelminthes Dicyemida Orthonectida