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The Spiralia
Spiralia
are a morphologically diverse clade of protostome animals, including within their number the molluscs, annelids, platyhelminths and other taxa.[1] The term Spiralia
Spiralia
is applied to those phyla that exhibit canonical spiral cleavage, a pattern of early development found in most (but not all) members of the Lophotrochozoa.[2] Distribution of spiralian development across phylogeny[edit] 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.[3] Lophotrochozoa
Lophotrochozoa
within Spiralia[edit] 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 the relationship between molluscs, annelids and lophophorates was found in 1995.[5] More recent research has established the Lophotrochozoa
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
Lophotrochozoa
as a whole.[3] 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.[7][8][9][10][11]

Protostomes (610)

Ecdysozoa

Spiralia

Gnathifera

Platytrochozoa (580)

Mesozoa

Rouphozoa

Gastrotricha

Platyhelminthes

Lophotrochozoa

Cycliophora

Mollusca

Lophophorata

Brachiozoa

Brachiopoda

Phoronida

Entoprocta

Ectoprocta

Nemertea

Annelida

Echiura

Clitellata

Siboglinidae

Sipuncula

References[edit]

^ Giribet G (April 2008). "Assembling the lophotrochozoan (=spiralian) tree of life". Philos. Trans. R. Soc. Lond. B Biol. Sci. 363 (1496): 1513–22. doi:10.1098/rstb.2007.2241. PMC 2614230 . PMID 18192183.  ^ "Explanations.html". Retrieved 2009-06-28.  ^ a b Hejnol, A. (4 August 2010). "A Twist in Time—The Evolution of Spiral Cleavage in the Light of Animal
Animal
Phylogeny". Integrative and Comparative Biology. 50 (5): 695–706. doi:10.1093/icb/icq103. PMID 21558233.  ^ Boyer, Barbara C.; Henry, Jonathan Q.; Martindale, Mark Q. (1 November 1996). "Dual Origins of Mesoderm in a Basal Spiralian: Cell Lineage Analyses in the Polyclad Turbellarian Hoploplana inquilina". Developmental Biology. 179 (2): 329–338. doi:10.1006/dbio.1996.0264. PMID 8903349.  ^ Halanych, K.; Bacheller, J.; Aguinaldo, A.; Liva, S.; Hillis, D.; Lake, J. (17 March 1995). "Evidence from 18S ribosomal DNA that the lophophorates are protostome animals". Science. 267 (5204): 1641–1643. doi:10.1126/science.7886451. PMID 7886451.  ^ Dunn, C.W.; Hejnol, A.; Matus, D.Q.; Pang, K.; Browne, W.E.; Smith, S.A.; Seaver, E.; Rouse, G.W.; Obst, M.; Sørensen, M. V.; Haddock, S.H.D.; Schmidt-Rhaesa, A.; Okusu, A.; Kristensen, R.M.; Wheeler, W.C.; Martindale, M.Q.; Giribet, G. (10 April 2008). "Broad phylogenomic sampling improves resolution of the animal tree of life". Nature. 452 (7188): 745–749. doi:10.1038/nature06614. PMID 18322464.  ^ Struck, Torsten H.; Wey-Fabrizius, Alexandra R.; Golombek, Anja; Hering, Lars; Weigert, Anne; Bleidorn, Christoph; Klebow, Sabrina; Iakovenko, Nataliia; Hausdorf, Bernhard (July 2014). "Platyzoan Paraphyly Based on Phylogenomic Data Supports a Noncoelomate Ancestry of Spiralia". Molecular Biology and Evolution. 31 (7): 1833–1849. doi:10.1093/molbev/msu143. PMID 24748651.  ^ Peterson, Kevin J.; Cotton, James A.; Gehling, James G.; Pisani, Davide (2008-04-27). "The Ediacaran emergence of bilaterians: congruence between the genetic and the geological fossil records". Philosophical Transactions of the Royal Society of London B: Biological Sciences. 363 (1496): 1435–1443. doi:10.1098/rstb.2007.2233. PMC 2614224 . PMID 18192191.  ^ "Phylogeny of platyzoan taxa based on molecular data (PDF Download Available)". ResearchGate. Retrieved 2017-10-01.  ^ Laumer, Christopher E.; Bekkouche, Nicolas; Kerbl, Alexandra; Goetz, Freya; Neves, Ricardo C.; Sørensen, Martin V.; Kristensen, Reinhardt M.; Hejnol, Andreas; Dunn, Casey W. (2015). "Spiralian Phylogeny Informs the Evolution of Microscopic Lineages". Current Biology. 25 (15): 2000–2006. doi:10.1016/j.cub.2015.06.068.  ^ Lu, Tsai-Ming; Kanda, Miyuki; Satoh, Noriyuki; Furuya, Hidetaka (2017-05-29). "The phylogenetic position of dicyemid mesozoans offers insights into spiralian evolution". Zoological Letters. 3: 6. doi:10.1186/s40851-017-0068-5. 

v t e

Extant Animal
Animal
phyla

Domain Archaea Bacteria Eukaryota (Supergroup Plant Hacrobia Heterokont Alveolata Rhizaria Excavata Amoebozoa Opisthokonta

Animal Fungi)

A n i m a l i a

Porifera (sponges)

Diploblasts (Eumetazoa)

Ctenophora
Ctenophora
(comb jellies)

ParaHoxozoa

Placozoa
Placozoa
(Trichoplax)

Planulozoa

Cnidaria
Cnidaria
(jellyfish and relatives)

Bilateria (Triploblasts)

(see below↓)

Bilateria

Xenacoelomorpha

Xenoturbellida (Xenoturbella) Acoelomorpha

acoels nemertodermatids

N e p h r o z o a

Deuterostomia

Chordata

lancelets tunicates craniates / vertebrates

Ambulacraria

Echinodermata (starfish and relatives) Hemichordata

acorn worms pterobranchs

P r o t o s t o m i a

Ecdysozoa

Scalidophora

Kinorhyncha
Kinorhyncha
(mud dragons) Priapulida
Priapulida
(penis worms)

N+L+P

Nematoida

Nematoda (roundworms) Nematomorpha
Nematomorpha
(horsehair worms)

L+P

Loricifera

Panarthropoda

Arthropoda (arthropods) Tardigrada (waterbears) Onychophora
Onychophora
(velvet worms)

S p i r a l i a

Gnathifera¹

Chaetognatha
Chaetognatha
(arrow worms) Gnathostomulida (jaw worms) Micrognathozoa (Limnognathia) Syndermata

Rotifera Acanthocephala

Platytrochozoa

R+M

Mesozoa

Orthonectida Dicyemida
Dicyemida
or Rhombozoa

Rouphozoa¹

Platyhelminthes
Platyhelminthes
(flatworms) Gastrotricha
Gastrotricha
(hairybacks)

Lophotrochozoa

Cycliophora (Symbion) Mollusca
Mollusca
(molluscs)

A+N

Annelida
Annelida
(ringed worms) Nemertea
Nemertea
(ribbon worms)

Lophophorata

Bryozoa

Entoprocta
Entoprocta
or Kamptozoa Ectoprocta
Ectoprocta
(moss animals)

Brachiozoa

Brachiopoda
Brachiopoda
(lamp shells) Phoronida
Phoronida
(horseshoe worms)

Major groups within phyla

Sponges

Calcareous Hexactinellid Demosponge Homoscleromorpha

Cnidarians

Anthozoa
Anthozoa
inc. corals Medusozoa
Medusozoa
inc. jellyfish Myxozoa

Vertebrates

Jawless fish Cartilaginous fish Bony fish Amphibians Reptiles/Birds Mammals

Echinoderms

Sea lilies Asterozoa
Asterozoa
inc. starfish Echinozoa

Nematodes

Chromadorea Enoplea Secernentea

Arthropods

Chelicerates/Arachnids Myriapods Crustaceans Hexapods/Insects

Platyhelminths

Turbellaria Trematoda Monogenea Cestoda

Bryozoans

Phylactolaemata Stenolaemata Gymnolaemata

Annelids

Polychaetes Clitellata Echiura

Molluscs

Gastropods Cephalopods Bivalves Chitons Tusk shells

Phyla with ≥5000 extant species bolded See also Diploblasts Monoblastozoa (nomen dubium)

¹Platyzoa

Taxon identifiers

Wd: Q1211307 EoL: 6551609

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