Adrioasteroid [1] ( lat. Edrioasteroidea ) is a class of extinct echinoderms . The living individual resembled a symmetrical disk with five-rayed symmetry or a pillow. A benthic animal attached to an inorganic or biological solid substrate (most often at the hard bottom or brachiopod shells) [2] .
| † adrioasteroid | |||||||||||||||||||||||||||||||||||||||||
 Foerstediscus | |||||||||||||||||||||||||||||||||||||||||
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| International Scientific Name | |||||||||||||||||||||||||||||||||||||||||
Edrioasteroidea Billings , 1858 | |||||||||||||||||||||||||||||||||||||||||
| Geochronology 521-273 Ma
◄ Nowadays◄ Cretaceous-Paleogene extinction◄ Triassic extinction◄ Perm mass extinction◄ Devonian extinction◄ Ordovician-Silurian extinction◄ Cambrian explosion | |||||||||||||||||||||||||||||||||||||||||
The oldest undisputed fossils of Edrioasteroidea are known in the Middle Cambrian sediments (3rd tier, 521-514 Ma ) of the ancient continent of Lawrence, and are among the oldest echinoderm fossils known. The last representatives of this class are known in the Permian period (Upper Kungurian Age ) [3] .
Some authors suggest that the mysterious Ediacaran organism Arkarua also belonged to this class, but this interpretation was not widely accepted [4] .
Content
Anatomy
The body plan for this class is extremely simple: the main body (theca), consists of many small plates, with a peripheral rim for attachment, and (in some species) zones of the stalk for expansion and contraction. Sometimes there is a rounded and attached to the body peripheral rim. The main feature was the presence of five hands or ambulacres located on the body and directed outward from being in the center of the mouth. Ambulacra could be curved or straight. Curved could be bent in one direction, or two of them in the opposite direction compared to the others. The ambulacres are constructed from the underlying floor of the slab, which serve as PAZ food products and protective lining of the food groove. The anus was located below the area of the mouth and was formed from small triangular plates that form a conical area. There were no plates on the bottom surface of the tech.
Edrioasteroid species differ in the ambulacrum curvature, the shape of the plates and the ornamentation. The mode of existence is motionless; were often attached with a stalk of small plates to hard objects, such as carbonate or shells. In some cases relic inclusions are noticed.
In the discocystinids, between the body and the peripheral rim can be extended and retracted; in this diverged. The peripheral rim became the base of the stem, which was attached to the surface. Under the body there was a lying zone , in which there was about 12 millimeters (0.47 ″) wide in the genus Giganticlavus , then the peduncule zone adjacent to the periphery of the rim of 12 millimeters (0.47 ″) [5] .
Classification
Very incomplete list of births:
- ? Arkarua
- ? A. adami (may be a Trilobozoan with pentamerous symmetry, and not an echinoderm at all)
- Walcottidiscus (oldest undisputed edrioasteroid, from the Middle Cambrian Burgess Shale community)
- W. typicalus
- Kailidiscus
- K. chinensis
- Edrioaster ( type genus )
- E. bigsbyi
- E. priscus
- Edriophus
- E. levis
- Paredriophus
- P. elongatus
- Totiglobus
- T. nimius
- T. lloydi
- Lebedodiscus
- Foerstediscus
- F. grandi
- F. splendens
- Cystaster
- C. stellatus
- Cryptogoleus
- C. chapmani
- Bellochthus
- Streptaster
- S. vorticellatus
- Cryptogoleus
- C. chapmani
- Carneyella
- C. pilea
- C. faberi
- C. ulrichi
- Isorophus
- I. cincinnatiensis
- Isorophusella
- Rectitriordo
- Agelacrinites
- Krama
- K. devonicum (Bassler), 1936
- Parakrama
- Hemicystites
- H. bohemica
- H. chapmani
- H. devonicus
- Neoisorophusella
- N. lanei
- N. berryi
- N. maslennikovi
- N. whitesidei
- Curvitriordo
- Thresherodiscus
- T. ramosa (Foerste, 1914)
- Postibulla
- P. westergaardi
- Parapostibulla
- P. belli
- P. graysoni
- Eopostibulla
- Pyrgopostibulla
- Torquerisediscus
- Cooperidiscus
- Dynocystis
- Stalticodiscus
- Ulrichidiscus
- Clavidiscus
- Discocystis
- Hypsiclavus
- Spiraclavus
- Giganticlavus
- Lispidecodus
- L. plinthotus (Kesling, 1967)
Gallery
Edriophus pigsgi , Middle Ordovician , Canada
Cystaster stellatus , Upper Ordovician, Northern Kentucky
Notes
- ↑ Fundamentals of Paleontology: A Handbook for Paleontologists and Geologists of the USSR: 15 t. / Ch. ed. Yu. A. Orlov . - M .: Nedra, 1964. - V. 10: Echinoderms, hemichord, pahonophores, bristle maxillaries. / ed. G. F. Hecker. - p. 28. - 384 s. - 3000 copies
- ↑ Streptaster vorticellatus
- ↑ Sumrall CD First Definite Record of Permian Edrioasteroids: Neoisorophusella maslennikovi n. sp. from the Kungurian of Northeast Russia (Eng.) // Journal of Paleontology : journal. - Paleontological Society , 2009. - Vol. 83 , no. 6 - P. 990-993 . - DOI : 10.1666 / 09-063.1 .
- ↑ Zamora S., Lefebvre B., Álvaro JJ et al. Chapter 13. Cambrian echinoderm diversity and palaeobiogeography (Eng.) // Geological Society, London, Memoirs: journal. - 2013. - Vol. 38 - P. 157-171 . - DOI : 10.1144 / M38.13 .
- ↑ Sumrall 1996
Links
Visited March 8, 2008.
- http://www.ucmp.berkeley.edu/echinodermata/edrioasteroidea.html University of California, Berkeley.
- http://drydredgers.org/edrio1.htm Compiled by Colin D. Sumrall.
- https://web.archive.org/web/20060830083438/http://www.tulane.edu/~csumral/Abstract Spiraclavus nacoensis , Edrioasteroid from Central Arizona by Colin D. Sumrall.
- http://www.science-art.com/image.asp?id=1357 Reconstruction by Emily Damstra.
- http://gsa.confex.com/gsa/2003AM/finalprogram/abstract_65113.htm Geological Society of America.
- https://web.archive.org/web/20060830083430/http://www.tulane.edu/~csumral/morph.html by Colin D. Sumrall