Spiralia

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Clade of protostomes with spiral cleavage during early development

title: "Spiralia" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["spiralia", "protostome-unranked-clades"] description: "Clade of protostomes with spiral cleavage during early development" topic_path: "general/spiralia" source: "https://en.wikipedia.org/wiki/Spiralia" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Clade of protostomes with spiral cleavage during early development ::

| fossil_range = Possible Ediacaran fossil | image = Spiralia clade.jpg | image_caption = | display_parents = 5 | taxon = Spiralia | authority = sensu Edgecombe et al. 2011 | subdivision_ranks = Clades | subdivision = *Gnathifera

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

Distribution of spiralian development across phylogeny

Members of the molluscs, annelids, platyhelminths and nemerteans have all been shown to exhibit spiral cleavage in its classical form. 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.

Lophotrochozoa within Spiralia

Previously, spiral cleavage was thought to be unique to the Spiralia in the strictest sense—animals such as molluscs and annelids, which exhibit classical spiral cleavage. The presence of spiral cleavage in animals such as platyhelminths could be difficult to correlate with some phylogenies.

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. More recent research has established the Lophotrochozoa as a superphylum within the Metazoa. With this understanding, the presence of spiral cleavage in polyclad platyhelminths, as well as the more traditional Spiralia, has led to the hypothesis that spiral cleavage was present ancestrally across the Lophotrochozoa as a whole. With the introduction of Platytrochozoa and Rouphozoa, the cladogram is as follows, with an indication approximately how many million years ago (Mya) the clades radiated into newer clades.

|1={{clade |1=Ecdysozoa [[File:Long nosed weevil edit.jpg|70px]] |2=Kimberella † |label3=Spiralia |3={{clade |1=Gnathifera [[File:Chaetoblack.png|70 px]] |label2=Platytrochozoa|sublabel2=580 mya |2={{clade |1={{clade |1=Mesozoa [[File:EB1911 Mesozoa - Rhopalura giardii.jpg|40px]] |label2=Rouphozoa |2={{clade |1=Gastrotricha [[File:Lepidodermella squamatum (cropped).jpg|60px]] |2=Platyhelminthes [[File:Sorocelis reticulosa.jpg|65px]] |label2=Lophotrochozoa |2={{clade |1=Annelida [[File:Polychaeta (no).JPG|60px]] |2=Mollusca [[File:Grapevinesnail 01.jpg|60px]] |label3=Kryptotrochozoa |3={{clade |label1=Lophophorata |1={{clade |label1=Brachiozoa |1={{clade |1=Brachiopoda [[File:LingulaanatinaAA (cropped).JPG|60px]] |2=Phoronida [[File:Phoronis Maria Grazia Montanucci2.jpg|50px]] |2={{clade |state1=dashed |1={{clade |1=Entoprocta [[File:Pedicellina cernua 001.png|60px]] |2=Cycliophora [[File:Symbion pandora (unlabelled).jpg|30px]] }} |2=Ectoprocta (Bryozoa) [[File:Plumatella repens from Haeckel Bryozoa drawing Commons2.jpg|60px]] |2=Nemertea [[File:Micrura verrilli Coe, 1901.png|40px]] An alternative phylogeny was given in 2019, with a basal grouping Mollusca with Entoprocta grouping named Tetraneuralia, and a second grouping of Nemertea with Platyhelminthes named Parenchymia as sister of Annelida. In their proposal and according to the original definition, Lophotrochozoa may become a senior synonym for Platytrochozoa.

In 2019 the Rouphozoa was recovered again as a basal Platytrochozoa clade.

A 2022 study supported the Trochozoa and Platyzoa hypotheses, as shown below. The same year another study placed bryozoans, entoproctans and cycliophorans in the group Polyzoa as one of the earliest branches among Lophotrochozoa.

|1=Ecdysozoa [[File:Long nosed weevil edit.jpg|70px]] |label2=Spiralia |2={{clade |label1=Trochozoa |1={{clade |1=Mollusca [[File:Grapevinesnail 01.jpg|60px]] |2={{clade |1=Nemertea [[File:Micrura verrilli Coe, 1901.png|40px]] |2=Annelida [[File:Polychaeta (no).JPG|60px]] |label3=Brachiozoa |3={{clade |1=Brachiopoda [[File:LingulaanatinaAA (cropped).JPG|60px]] |2=Phoronida [[File:Phoronis Maria Grazia Montanucci2.jpg|50px]] }} }} }} |2={{clade |1={{clade |1=Bryozoa [[File:Plumatella repens from Haeckel Bryozoa drawing Commons2.jpg|60px]] |2={{clade |1=Entoprocta [[File:Pedicellina cernua 001.png|60px]] |2=Cycliophora [[File:Symbion pandora (unlabelled).jpg|30px]] }} }} |label2=Platyzoa |2={{clade |barbegin1=blue |1=Gastrotricha [[File:Lepidodermella squamatum (cropped).jpg|60px]] |2={{clade |bar1=blue |1=Gnathifera [[File:Chaetoblack.png|70 px]] |2={{clade |bar1=blue |1=Platyhelminthes [[File:Sorocelis reticulosa.jpg|65px]] |barend1=blue |label2=Mesozoa |2={{clade |1=Dicyemida [[File:Dicyema macrocephalum.png|40px]] |2=Orthonectida [[File:EB1911 Mesozoa - Rhopalura giardii.jpg|40px]] }} }} }}|grouplabel1=Platyzoa }} }} }} }}}}

References

References

  1. Telford, Maximilian J.. (2019). "Evolution: Arrow Worms Find Their Place on the Tree of Life". [[Current Biology]].
  2. {{The Rise and Fall of the Ediacaran Biota. Fedonkin, M.A.
  3. Giribet, G.. (April 2008). "Assembling the lophotrochozoan (=spiralian) tree of life". [[Philosophical Transactions of the Royal Society B: Biological Sciences]].
  4. "Explanations.html".
  5. Hejnol, A.. (4 August 2010). "A Twist in Time—The Evolution of Spiral Cleavage in the Light of Animal Phylogeny". [[Integrative and Comparative Biology]].
  6. Boyer, Barbara C.. (1 November 1996). "Dual Origins of Mesoderm in a Basal Spiralian: Cell Lineage Analyses in the Polyclad Turbellarian ''Hoploplana inquilina''". [[Developmental Biology]].
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  9. (July 2014). "Platyzoan Paraphyly Based on Phylogenomic Data Supports a Noncoelomate Ancestry of Spiralia". [[Molecular Biology and Evolution]].
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  11. (2014). "Deep Metazoan Phylogeny: The Backbone of the Tree of Life". Walter de Gruyter GmbH.
  12. (2015). "Spiralian Phylogeny Informs the Evolution of Microscopic Lineages". [[Current Biology]].
  13. (2017-05-29). "The phylogenetic position of dicyemid mesozoans offers insights into spiralian evolution". Zoological Letters.
  14. (2017-12-04). "Nemertean and phoronid genomes reveal lophotrochozoan evolution and the origin of bilaterian heads". [[Nature Ecology and Evolution]].
  15. (2019-01-10). "A New Spiralian Phylogeny Places the Enigmatic Arrow Worms among Gnathiferans". [[Current Biology]].
  16. (1995-03-17). "Evidence from 18S ribosomal DNA that the lophophorates are protostome animals". Science.
  17. (2019). "The evolution of molluscs: The evolution of molluscs". Biological Reviews.
  18. (2019-07-10). "Revisiting metazoan phylogeny with genomic sampling of all phyla". [[Proceedings of the Royal Society B: Biological Sciences]].
  19. (2022-07-13). "Different phylogenomic methods support monophyly of enigmatic 'Mesozoa' (Dicyemida + Orthonectida, Lophotrochozoa)". Proceedings of the Royal Society B: Biological Sciences.
  20. [https://www.science.org/doi/10.1126/sciadv.abo4400 Polyzoa is back: The effect of complete gene sets on the placement of Ectoprocta and Entoprocta - Science]

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spiraliaprotostome-unranked-clades