Ecdysozoa

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Ecdysozoa
Temporal range: Cambrian - Recent Molecular clock indicates a possible Ediacaran origin[1]
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Subkingdom: Eumetazoa
Clade: ParaHoxozoa
Clade: Bilateria
Clade: Nephrozoa
(unranked): Protostomia
Superphylum: Ecdysozoa
Aguinaldo et al., 1997
Phyla

Ecdysozoa (

phenotypes.[5] This clade, that is, a group consisting of a common ancestor and all its descendants, was formally named by Aguinaldo et al. in 1997, based mainly on phylogenetic trees constructed using 18S ribosomal RNA genes.[6]

A large study in 2008 by Dunn et al. strongly supported the monophyly of Ecdysozoa.[7]

The group Ecdysozoa is supported by many morphological characters, including growth by ecdysis, with moulting of the cuticle – without mitosis in the epidermis – under control of the prohormone ecdysone, and internal fertilization.[8]

The group was initially contested by a significant minority of biologists. Some argued for groupings based on more traditional taxonomic techniques,[9] while others contested the interpretation of the molecular data.[10][11]

Etymology

The name Ecdysozoa is "scientific" Greek, derived from ἔκδυσις (ékdusis) "shedding" + ζῷον (zôion) "animal".

Characteristics

See also:
List of bilaterial animal orders

The most notable characteristic shared by ecdysozoans is a three-layered

spiral cleavage as in most other protostomes. Ancestrally, the group exhibited sclerotized teeth within the foregut, and a ring of spines around the mouth opening, though these features have been secondarily lost in certain groups.[13][14] A respiratory and circulatory system is only present in onychophorans
and arthropods (often absent in smaller arthropods like mites); in the rest of the groups, both systems are missing.

Phylogeny

The Ecdysozoa include the following phyla:

Nematoda, and Nematomorpha. A few other groups, such as the gastrotrichs, have been considered possible members but lack the main characters of the group, and are now placed elsewhere. The Arthropoda, Onychophora, and Tardigrada have been grouped together as the Panarthropoda because they are distinguished by segmented body plans.[15] Dunn et al. in 2008 suggested that the tardigrada could be grouped along with the nematodes, leaving Onychophora as the sister group to the arthropods.[7] The non-panarthropod members of Ecdysozoa have been grouped as Cycloneuralia but they are more usually considered paraphyletic in representing the primitive condition from which the Panarthropoda evolved.[16]

A modern consensus phylogenetic tree for the protostomes is shown below.[17][18][19][20][21][22] It is indicated when approximately clades radiated into newer clades in millions of years ago (Mya); dashed lines show especially uncertain placements.[23]

The phylogenetic tree is based on Nielsen et al.[24] and Howard et al.[25]

 Bilateria 

Xenacoelomorpha

 Nephrozoa 

Deuterostomia

 
Protostomia
 
 Ecdysozoa 

Spiralia

Kimberella †

610 mya

Older alternative groupings

Articulata hypothesis

The grouping proposed by Aguinaldo et al. is almost universally accepted, replacing an older hypothesis that

Annelida,[26] though later considered them unrelated.[27]
Inclusion of the
James Lake for the discovery of the New Animal Phylogeny consisting of the Ecdysozoa, the Lophotrochozoa, and the Deuterostomia.[31]

Coelomata hypothesis

Before Aguinaldo's Ecdysozoa proposal, one of the prevailing theories for the evolution of the

Eucoelomata (true coelom). Adoutte and coworkers were among the first to strongly support the Ecdysozoa.[32] With the introduction of molecular phylogenetics, the coelomate hypothesis was abandoned, although some molecular, phylogenetic support for the Coelomata continued until as late as 2005.[33]

References

  1. ^
    S2CID 246494357
    . Retrieved 2023-07-30.
  2. S2CID 251646316
    .
  3. PMID 33228518
    .
  4. PMID 18192181
    .
  5. doi:10.1093/sysbio/41.3.305
    .
  6. S2CID 4334033
    .
  7. ^
    S2CID 4397099
    .
  8. ISBN 9780198571810
  9. ISBN 978-0-19-850682-9
    .
  10. ^
    PMID 11985779
    .
  11. doi:10.1111/j.1439-0469.1999.tb00985.x
    .
  12. ISBN 0-03-056747-5
    .
  13. S2CID 205244325
    .
  14. ^ The mouth apparatus of the Cambrian gilled lobopodian Pambdelurion whittingtoni
  15. ^ "Panarthropoda". Paleos (palaeos.com). Invertebrates. Archived from the original on 2007-02-07. Retrieved 17 February 2007.
  16. S2CID 22823313
    .
  17. S2CID 32169826
    .
  18. PMID 28377584
    .
  19. S2CID 205239797
    .
  20. ^ "Palaeos Metazoa: Ecdysozoa". palaeos.com. Retrieved 2017-09-02.
  21. PMID 26605063
    .
  22. ISBN 0-19-850682-1
    .
  23. PMID 18192191
    .
  24. S2CID 52067372
    .
  25. S2CID 246494357
    .
  26. S2CID 1416582
    .
  27. ISBN 978-0-19-960603-0
    .
  28. doi:10.1046/j.1439-0469.2001.00168.x
    . — in support of clade Ecdysozoa
  29. doi:10.1046/j.1439-0469.2001.00177.x
    .
  30. PMID 18192193
    .
  31. ^ "The Darwin-Wallace Medal" (Press release). The Linnean Society of London. Retrieved 28 February 2018.
  32. PMID 10781043
    .
  33. PMID 15703245
    .

External links

Wikispecies has information related to Ecdysozoa.
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