Megacheira

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Megacheira
Temporal range: Cambrian Stage 3–Middle Cambrian Possible Silurian and Devonian records
Alalcomenaeus (top left), Fortiforceps (top right), Haikoucaris (middle), Leanchoilia (bottom left) and Yohoia (bottom right).
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Class: †Megacheira
Hou and Bergström, 1997
Groups

Megacheira ("great hands", also historically great appendage arthropods) is an extinct class of predatory

stem-group euarthropods, or stem-group chelicerates.[2] The homology of the great appendages to the cephalic appendages of other arthropods is also controversial. Uncontested members of the group were present in marine environments worldwide from the lower to middle Cambrian
.

Morphology

Comparison of megacheiran great appendages
Movement range of the great appendage of Yohoia

Megacheirans are defined by their possession of

exites.[6]

Taxonomy

Several subdivisions within the group are recognised including Jianfengiidae (including

paraphyletic.[3]

radiodont was later suggested to be a member of this group.[7][8][9] Possible megacheirans include Enalikter described from the Silurian of the United Kingdom, and Bundenbachiellus from the Early Devonian of Germany;[10][11] due to their possession of great appendage-like cephalic appendages. However, their relationship to megacheirans has been questioned, due to the uncertain homology of their appendages.[12] Kootenichela has been suggested to be a chimera of various arthropod taxa.[3] Previous inclusion of some "bivalved" genera such as Forfexicaris, Ovalicephalus, and Occacaris to Megacheira was questioned by later investigations.[13] The Late Cambrian Orsten taxon Oelandocaris typically considered to be a crustacean relative, has also been suggested in some studies to be a megacheiran.[14]

Relationship to other arthropods

Main article: Arthropod head problem

Megacheirans are either suggested to be stem-group

radiodonts. This identity is disputed, with other authors suggesting that the frontal appendages of radiodonts are homologous to the labrum of modern arthropods.[3]

References

  1. doi:10.1111/j.1096-3642.2009.00562.x
    .
  2. ^
    S2CID 243269510
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  3. ^
    PMID 31914921
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  4. ^
    doi:10.1111/j.1475-4983.2011.01124.x
    .
  5. S2CID 86443516
    .
  6. PMID 34330912
    .
  7. ISSN 0024-4082
    .
  8. ISBN 9781118896389
    .
  9. S2CID 206517995
    .
  10. PMID 24452026
    .
  11. PMC 4375861
    .
  12. S2CID 243269510
    .
  13. PMID 27989966
    .
  14. S2CID 4454526
    .
  15. ISSN 1502-3931
    .
  16. PMID 19557680
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  17. S2CID 82841481
    .
  18. S2CID 4456458
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  19. S2CID 220057956
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  20. S2CID 4456458
    .
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