Spiralia
| Spiralia Temporal range:
| |
|---|---|
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Scientific classification 
| |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Subkingdom: | Eumetazoa |
| Clade: | ParaHoxozoa |
| Clade: | Bilateria |
| Clade: | Nephrozoa |
| (unranked): | Protostomia |
| (unranked): | Spiralia sensu Edgecombe et al. 2011 |
| Clade | |
The Spiralia are a morphologically diverse
spiral cleavage, a pattern of early development found in most (but not all) members of the Lophotrochozoa.[2]
Distribution of spiralian development across phylogeny
Members of the
spiral cleavage in at least a portion of their constituent species, although evidence for this is sparse.[3]
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.[4]
Evidence of a close relationship between
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.[5] More recent research has established the Lophotrochozoa as a superphylum within the Metazoa.[6]
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.[3]
With the introduction of Rouphozoa, the cladogram is as follows, with an indication approximately how many million years ago (Mya) the clades radiated into newer clades.[7][8][9][10][11][12]
Protostomia
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| 610 mya |
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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.[13][14][15][16]
| Protostomia
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In 2019 the
Rouphozoa was recovered again as a basal Platytrochozoa clade.[17]
A 2022 study supported the Trochozoa and Platyzoa hypotheses, as shown below.[18] The same year another study placed bryozoans, entoproctans and cycliophorans in the group Polyzoa as one of the earliest branches among Lophotrochozoa.[19]
Protostomia
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References
- PMID 18192183.
- ^ "Explanations.html". Archived from the original on 2013-02-07. Retrieved 2009-06-28.
- ^ PMID 21558233.
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- ^ Hankeln, Thomas; Wey-Fabrizius, Alexandra; Herlyn, Holger; Witek, Alexander; Weber, Mathias; Nesnidal, Maximilian; Struck, Torsten (2014). "Phylogeny of platyzoan taxa based on molecular data". In Wägele, J. Wolfgang; Bartolomaeus, Thomas (eds.). Deep Metazoan Phylogeny: The Backbone of the Tree of Life. Walter de Gruyter GmbH. pp. 105–125.
- PMID 26212884.
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- S2CID 12196991.
- PMID 29931833.
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- PMID 35858055.
- ^ Polyzoa is back: The effect of complete gene sets on the placement of Ectoprocta and Entoprocta - Science