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Disparida

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Disparida
Temporal range: Tremadocian–Middle Permian
Synbathocrinus from the Mississippian of Missouri, USA
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Echinodermata
Class: Crinoidea
Infraclass: Inadunata
Parvclass: †Disparida
Moore & Laudon, 1943
Orders[1]

Disparida is an parvclass of extinct marine animals in the class Crinoidea.[2][3][1] Disparids are a speciose and morphologically diverse group of crinoids distinguished by their monocyclic calyx and slender arms without pinnules. They range from the Early Ordovician (Tremadocian) to Middle Permian, reaching their highest diversity during the Late Ordovician.[4]

While many disparids had a generalized shape typical of other stalked crinoids, some subgroups achieved strange forms. The long-lasting Calceocrinidae were recumbent forms, with a flattened crown bent back onto a stalk which rested on the seafloor. Other unusual disparid families include the armless Zophocrinidae, the spiral-armed Myelodactylidae, and the diminutive, simplified Pisocrinidae. Disparids have long been classified by the structure of their radial plates and different planes of symmetry, but a cumulative phylogenetic approach has failed to confirm the validity of many proposed subgroups. Nevertheless, Disparida itself is well-supported as a distinct monophyletic group.[4]

Major traits of Disparida include:[1][5]

  • Small monocyclic calyx, without interbasal plates. Radial plates are proportionally large and may be compound (with multiple components), while basal plates are often reduced.
  • Proximal branchial plates tend to fuse with their respective radials.
  • Thin, uniserial arms without pinnules. Branching is typically frequent.
  • Redevelopment of prominent bilateral symmetry via an axis aligned to one of the five rays making up the crown. This axis of symmetry may lie along the E ray (homocrinoid symmetry), D ray (heterocrinoid symmetry), C ray (isocrinoid symmetry), or A ray (crinoid/belemnocrinoid symmetry, which is developed to a lesser degree in other crinoids).
  • Posterior plates lie above the C radial.

List of families and genera

[edit]

Disparida classification is undergoing revision. Many proposed families are paraphyletic or polyphyletic.[5][6][4]

Family Acolocrinidae

Family Allagecrinidae

Family Alphacrinidae

Family Anamesocrinidae

Family Anomalocrinidae

Family Aptocrinidae

Family Athenacrinidae

Family Belemnocrinidae

Family Calceocrinidae

Family Catillocrinidae

Family Cincinnaticrinidae (i.e. Heterocrinidae, paraphyletic / polyphyletic)

Family Columbicrinidae

Family Dulkumocrinidae

Family Eustenocrinidae

Family Haplocrinitidae

Family Homocrinidae (paraphyletic / polyphyletic)

Family Iocrinidae (paraphyletic)

Family Maennilicrinidae

Family Myelodactylidae

Family Pisocrinidae

Family Pygmaeocrinidae (polyphyletic)

Family Synbathocrinidae

Family Tetragonocrinidae

Family Zophocrinidae

Incertae sedis

References

[edit]
Wikispecies has information related to Disparida.
  1. ^ a b c Wright, David F.; Ausich, William I.; Cole, Selina R.; Peter, Mark E.; Rhenberg, Elizabeth C. (2017). "Phylogenetic taxonomy and classification of the Crinoidea (Echinodermata)". Journal of Paleontology. 91 (4): 829–846. doi:10.1017/jpa.2016.142. ISSN 0022-3360.
  2. ^ W. I. Ausich, D. F. Wright, S. R. Cole and J. M. Koniecki. 2018. Disparid and hybocrinid crinoids (Echinodermata) from the Upper Ordovician (lower Katian) Brechin Lagerstätte of Ontario. Journal of Paleontology 92(5):850-871 [S. Cole/S. Cole]
  3. ^ Y. Y. Mao, G. D. Webster, W. I. Ausich, Y. Li, Q. L. Wang and M. Reich. 2018. A new crinoid fauna from the Taiyuan Formation (early Permian) of Henan, North China. Journal of Paleontology 92:1066-1080
  4. ^ a b c Ausich, William I. (2018-12-01). "Morphological paradox of disparid crinoids (Echinodermata): phylogenetic analysis of a Paleozoic clade". Swiss Journal of Palaeontology. 137 (2): 159–176. doi:10.1007/s13358-018-0147-z. ISSN 1664-2384.
  5. ^ a b Moore, Raymond C. (1978). Moore, Raymond C.; Teichert, Curt (eds.). Part T, Echinodermata 2, Crinoidea, vol. 2. Treatise on invertebrate paleontology. By Georges Ubaghs, R. C. Moore, H. Wienberg Rasmussen, N. Gary Lane, Albert Breimer, H. L. Strimple, J. C. Brower, Russell M. Jeffords, James Sprinkle, R. E. Peck, D. B. Macurda Jr., D. L. Meyer, Michel Roux, Hertha Sieverts-Doreck, R. O. Fay, and R. A. Robison. Boulder, CO and Lawrence, KS: University of Kansas and Geological Society of America. ISBN 978-0-8137-3021-9. OCLC 531991.
  6. ^ "PBDB". paleobiodb.org. Retrieved 2020-05-16.


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