Spiralia

Spiralia is a group of protostome animals, it has many animals with a common ancestor like molluscs, annelids, platyhelminths and more groups.^[3] The term Spiralia comes from the fact that they have spiral cleavage, in their embryos.^[4]

Spiralia Temporal range: Cambrian–Recent[1] PreꞒ Ꞓ O S D C P T J K Pg N Possible Ediacaran fossil[2]
Scientific classification
Kingdom:	Animalia
Subkingdom:	Eumetazoa
Clade:	ParaHoxozoa
Clade:	Bilateria
Clade:	Nephrozoa
Clade:	Protostomia
(unranked):	Spiralia sensu Edgecombe et al. 2011
Clades
Gnathifera Platytrochozoa

Embryo growth

Members of the molluscs, annelids, platyhelminths and nemerteans all have spiral cleavage in their embryos. Other groups like rotifers, brachiopods, phoronids, gastrotrichs, and bryozoans do not do it, but might have had it in the past.^[5]

Family tree of Spiralians

This is a version of the family tree of Spiralians.^{[6][7][8][9][10][11][12]}

	Ecdysozoa Kimberella † Spiralia Gnathifera Platytrochozoa Mesozoa Rouphozoa Gastrotricha Platyhelminthes Lophotrochozoa Annelida Mollusca Kryptotrochozoa Lophophorata Brachiozoa Brachiopoda Phoronida Entoprocta Cycliophora Ectoprocta (Bryozoa) Nemertea

In 2019 this new version of the family tree was made.^[13][14][15]

Protostomia	Ecdysozoa  Spiralia (s.l.) / Gnathifera  Lophotrochozoa /   Tetraneuralia    Mollusca Entoprocta     Gastrotricha  Lophophorata      Ectoprocta Phoronida Brachiopoda Annelida  Parenchymia    Platyhelminthes Nemertea

In 2022 scientists found this family tree.^[16]

Protostomia	Ecdysozoa Spiralia Trochozoa Mollusca Nemertea Annelida Brachiozoa Brachiopoda Phoronida Bryozoa Entoprocta Cycliophora Platyzoa Gastrotricha Gnathifera Platyhelminthes Mesozoa Dicyemida Orthonectida