Echinodermata
From Palaeos.org
| DEUTEROSTOMIA | |
| Taxonomy | Phylogeny |
Domain: Eukarya
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Bilateria `--Deuterostomia |--Vetulicolia |--Yunnanozoa |--+--Xenoturbella | `--Ambulacraria | |?--Dinomischida | |--Hemichordata | `--+--Vetulocystidae | `--+--Stylophora | `--+--Soluta | `--+--Cincta | `--+--Ctenocystoidea | `--+--Helicoplacoidea | `--+--Edrioasteroidea | `--Echinodermata `--Chordata |--Urochordata `--+--Cephalochordata `--Craniata `--Vertebrata |
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Deuterostomia topics: Fossil Record | Characteristics | The Fall and Rise of Orders of Symmetry | Ecology and Lifestyle | Links | References |
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Contents |
Introduction
The echinoderms (or "spiny skins") are a diverse group of completely marine animals. They are known from the Cambrian to the Recent and are found in shallow marine waters as well as the deep abyssal plains.
They have a soft body encased in a hard rigid shell or exoskeleton (called a test) made of individual plates (or ossicles) made up of numerous thin plates. Many echinoderms have spines covering their test (e.g. the sea urchin). This group includes such familiar sea-shore creatures as starfish and sea urchins, as well as a number of less known types, and a whole range of paleozoic forms that are no longer around. There are some 6000 recent species, distributed among five classes. But these are only a small fraction of the number and diversity of types that lived in past ages, especially during the Paleozoic era when the group was at its height.
The most distinctive thing about echinoderm appearance is their pentameral - that is, a five fold - radial symmetry. In other words, their body is structured on a five-fold plan, with rays or arms in fives or multiples of five, as shown for example with the familiar starfish with its five arms.
Echinoderms also have a complex and unique water-vascular (or ambulacral) system; a hydrostatic skeleton of internal water-filled canals. This evolved originally as a food collecting and transporting device, but in some echinoderms like starfish and sea urchins is used primarily for movement by means of suckered "tube feet". It can also be used to grip objects and even in the case of starfish apply tremendous force to price open clams, upon which those animals feed.
Echinoderms larvae have bilateral symmetry (having a definite front and rear) while as adults this is lost. This shows that they evolved from normal ancestors and only secondarily reverted to radial symmetry.
Many early echinoderms were not pentameral at all, and had strange armoured shapes. Some types were able to crawl by nudging themselves along the sea floor with a sort of "tail".
Strange as it may seem, echinoderms are actually distant cousins of vertebrates. Both share a common type of embryonic development, and are grouped under the infrakingdom Deuterostomia.
| ECHINODERMATA | |
| Taxonomy | Phylogeny |
Superphylum:Deuterostomia
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o Deuterostomia `--+--Helicoplacoidea `--+--Camptostroma `--+--Thecocystidae `--+--Edrioasteroidea `--+--Cyclocystoidea `--+==Eocrinoidea | `==Cystoidea | `--Blastoidea `--+--o Eleutherozoa | |--o Asterozoa | | |--Ophioxenikos | | `--+--Asteroidea | | `--Ophiuroidea | `--o Echinozoa | |--Echinoidea | `--+--Holothuroidea | `--Ophiocistioidea `--+--Homalozoa `--+--Echmatocrinus `--Crinoidea |
Classification
The following classification, based on Linnaean lines, may not necessarily follow current developments in echinoderm phylogeny. For a more recent phylogeny, see the following section and also (for basal and other forms that are stem group echinoderms rather than crown group echinoderms) see the phylogeny at the top of this page.
- Phylum Echinodermata
- Subphylum Blastozoa
- Class Eocrinoidea (Cambrian - Silurian, 30-32 genera)
- Class Parablastoidea (Ordovician, 3 genera)
- Class Rhombifera = Cystoidea]] in part (Ordovician - Devonian, 60 genera)
- Class Diploporita = Cystoidea in part (Ordovician - Devonian, 42 genera)
- Class Blastoidea (Silurian - Permian, 95 genera)
- Subphylum Crinozoa
- Class Crinoidea - sea lilies (Cambrian? Early Ordovician - Recent, 1005 genera)
- Class Paracrinoidea (Ordovician - Silurian, 13-15 genera)
- Subphylum Echinozoa
- Class Echinoidea (Sea Urchins) (Ordovician - Recent, 765 genera)
- Class Holothuroidea (Sea Cucumbers) (Ordovician - Recent, 200 genera)
- Class Edrioasteroidea (Early Cambrian - Carboniferous, 35 genera)
- Class Edrioblastoidea (Ordovician, 1 genus)
- Class Helicoplacoidea (Cambrian, 3 genera)
- Class Cyclocystoidea (Ordovician - Devonian, 8 genera)
- Subphylum Asterozoa (= Stelleroidea)
- Class Asteroidea - starfish - (Early Ordovician - Recent, 430 genera)
- Class Ophiuroidea - Brittle Stars -(Ordovician - Recent, 325 genera)
- Subphylum Blastozoa
Phylogeny
Dendrogram
There are a number of deeply conflicting suggestions about the true shape of echinoderm phylogeny. I have here attempted to conflate the various options reviewed in Mooi (2001), but in attempting to reconcile the irreconcilable I have no doubt introduced points that would probably be unacceptable to all sides. As always, any such errors are entirely my own.
<==Echinodermata [Thecoidea] | i. s.: Xyloplax [Concentricycloidea, Concentricyclomorpha] | `--X. medusiformis | Ophioplocus japonicus | Agelacrinidae | |--Hemicystites | `--Agelacrinites lebouri | Haplozoa | |--Cymbionites | `--Peridionites |--Arkarua `--+--Helicoplacoidea `--+--Camptostroma [Camptostromatoidea] `--+--Thecocystidae [Stromatocystitoidea] | |--Stromatocystites balticus | |--Thecocystis | |--Cystaster | `--Cyathocystis | |--C. corallum Jaekel 1918 | `--C. plantinae `--+--Edrioasteroidea | | i. s.: Dinocystis | |--Isophorida | `--Edrioaster [Edrioasterida] `--+--Cyclocystoidea `--+--Eleutherozoa `--Blastozoa [Eocrinoidea] | i. s.: Amygdalocystis | Comarocystites | Akadocrinus Prokop 1962 (see below for synonymy) | Malocystites [Deviata, Malocystidae] | Lichenoides [Lichenoidae] | `--L. priscus | Atava | |--Ascocystites [Ascocystidae] | | `--A. barrandei Jaekel 1918 | `--Eocrinidae | |--Acanthocystites briareus | |--Cigara dusli | |--Eocystis | |--Protocystites | `--Eocrinus Jaekel 1918 | `--*E. longidactylus [=Eocystites longidactylus] |--Lepidocystis [Imbricata, Lepidocystoidea] `--+--Gogia | |--G. granulosa | |--G. palmeri | `--G. prolifica `--+--Balantiocystis `--Cystoidea [Anthodiata, Cystidea] | i. s.: Ascocrinus Barrande 1887 |--+--Diploporita | `--+--+--Cambrocrinus regularis | | `--Ridersia watsonae | `--+--Rhombifera | | |--Dichoporita | | `--Fistuliporita | `--Crinozoa | |--Crinoidea | `--Paracrinoidea [Paracrinozoa] `--+--Blastocystis Jaekel 1918 (see below for synonymy) | `--*B. carchariaedeus (see below for synonymy) `--+--Amygdalocystites |--Lepadocystis `--Blastoidea
Akadocrinus Prokop 1962 [incl. Compsocrinus Perner in Zelizko 1911 (n. n.) non Miller 1883]
Blastocystis Jaekel 1918 [Blastocystidae, Parablastida, Parablastoidea]
*Blastocystis carchariaedeus [=Blastoidocrinus carchariaedeus]
* Type species of generic name indicated
References
Anon. 1978. Unassigned taxa. In Treatise on Invertebrate Paleontology pt. T. Echinodermata 2. Crinoidea (R. C. Moore & C. Teichert, eds.) vol. 3 p. T928. The Geological Society of America, Inc.: Boulder (Colorado), and The University of Kansas: Lawrence (Kansas).
Ausich, W. I. 1999. Origin of crinoids. In Echinoderm Research 1998 (M. D. Candia Carnevali & F. Bonasoro, eds.) pp. 237-242. A. A. Balkema: Rotterdam.
Boczarowski, A. 2001. Isolated sclerites of Devonian non-pelmatozoan echinoderms. Palaeontologia Polonica 59: 1-219.
Cameron, C. B., J. R. Garey & B. J. Swalla. 2000. Evolution of the chordate body plan: New insights from phylogenetic analyses of deuterostome phyla. Proceedings of the National Academy of Sciences of the USA 97 (9): 4469-4474.
Jaekel, O. 1918. Phylogenie und System der Pelmatozoen. Paläontologische Zeitschrift 3: 1-128.
Miller, S. A., & J. P. Harley. 1996. Zoology (3rd ed.) Wm. C. Brown Publishers: Dubuque (Iowa).
Mooi, R. 2001. Not all written in stone: Interdisciplinary syntheses in echinoderm paleontology. Canadian Journal of Zoology 79: 1209-1231.
Sprinkle, J., & R. A. Robison. 1978. Addendum to subphylum Homalozoa: Ctenocystoids. In Treatise on Invertebrate Paleontology pt. T. Echinodermata 2. Crinoidea (R. C. Moore & C. Teichert, eds.) vol. 3 pp. T998-T1002. The Geological Society of America, Inc.: Boulder (Colorado), and The University of Kansas: Lawrence (Kansas).
Ubaghs, G. 1978a. Classification of the echinoderms. In Treatise on Invertebrate Paleontology pt. T. Echinodermata 2. Crinoidea (R. C. Moore & C. Teichert, eds.) vol. 1 p. T359-T367. The Geological Society of America, Inc.: Boulder (Colorado), and The University of Kansas: Lawrence (Kansas).
Ubaghs, G. 1978b. Camerata. In Treatise on Invertebrate Paleontology pt. T. Echinodermata 2. Crinoidea (R. C. Moore & C. Teichert, eds.) vol. 2 pp. T408-519. The Geological Society of America, Inc.: Boulder (Colorado), and The University of Kansas: Lawrence (Kansas).
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