Homalozoa: Difference between revisions
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The '''Homalozoa''' are extinct, [[Paleozoic]] [[echinoderms]] that lacked the typical pentamer body form. Instead all homalozoans were markedly asymmetric. Homalozoans are extremely variable in forms, but they all were sessile animals. The body ([[theca]]) was covered with [[calcite]] plates with a number of openings. Their form is in some cases so unusual that it is unclear which openings are to be considered as mouth and anus. Many of them were stalked, similar to sea lilies ([[crinoid]]s), but often their bodies were bent over, so that the mouth and anus projected forwards rather than upwards. Some forms, especially stylophorans, rested flat on the sea floor<ref name=Lefebvre2003>{{cite journal|last=Lefebvre|first=Bertrand|title=Functional Morphology of Stylophoran Echinoderms|journal=Palaeontology|year=2003|volume=46|issue=3|pages=511–555|doi=10.1111/1475-4983.00309}}</ref>. In some forms the single ray ([[brachiole]] or [[aulacophore]]) possessed an [[ambulacral]] groove<ref name=IZ>{{cite book |author= Barnes, Robert D. |year=1982 |title= Invertebrate Zoology |publisher= Holt-Saunders International |location= Philadelphia, PA|page= 1011|isbn= 0-03-056747-5}}</ref>. It has been claimed that some forms possessed [[gills]] and [[gill slit]]s<ref name=Dominguez2002>{{cite journal|last=Dominguez|first=Patrício|coauthors=Jacobson, Antone G.; Jefferies, Richard P. S.|title=Paired gill slits in a fossil with a calcite skeleton|journal=Nature|year=2002|volume=417|issue=6891|pages=841–844|doi=10.1038/nature00805|pmid=12075349}}</ref>. |
The '''Homalozoa''' are extinct, [[Paleozoic]] [[echinoderms]] that lacked the typical pentamer body form. Instead all homalozoans were markedly asymmetric. Homalozoans are extremely variable in forms, but they all were sessile animals. The body ([[theca]]) was covered with [[calcite]] plates with a number of openings. Their form is in some cases so unusual that it is unclear which openings are to be considered as mouth and anus. Many of them were stalked, similar to sea lilies ([[crinoid]]s), but often their bodies were bent over, so that the mouth and anus projected forwards rather than upwards. Some forms, especially stylophorans, rested flat on the sea floor<ref name=Lefebvre2003>{{cite journal|last=Lefebvre|first=Bertrand|title=Functional Morphology of Stylophoran Echinoderms|journal=Palaeontology|year=2003|volume=46|issue=3|pages=511–555|doi=10.1111/1475-4983.00309}}</ref>. In some forms the single ray ([[brachiole]] or [[aulacophore]]) possessed an [[ambulacral]] groove<ref name=IZ>{{cite book |author= Barnes, Robert D. |year=1982 |title= Invertebrate Zoology |publisher= Holt-Saunders International |location= Philadelphia, PA|page= 1011|isbn= 0-03-056747-5}}</ref>. It has been claimed that some forms possessed [[gills]] and [[gill slit]]s<ref name=Dominguez2002>{{cite journal|last=Dominguez|first=Patrício|coauthors=Jacobson, Antone G.; Jefferies, Richard P. S.|title=Paired gill slits in a fossil with a calcite skeleton|journal=Nature|year=2002|volume=417|issue=6891|pages=841–844|doi=10.1038/nature00805|pmid=12075349}}</ref>. |
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==Solute== |
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Solutes are an extinct type of [[invertebrate]] marine animal, from the [[Paleozoic]] era. They are carpoid [[echinoderm]]s ([[Homalozoa]]). Unlike many other types of echinoderm, they lack radial symmetry (such as the five limbs of a [[starfish]]). <ref> A. B. Smith ''Deuterostome phylogeny and the interpretation of problematic fossil echinoderms'', page 543-544 in Thomas Heinzeller, James H. Nebelsick ''Echinoderms: München'', CRC Press, 2004 ISBN 0415364817, </ref> |
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<ref>{{cite doi|10.1002/gj.1018}}</ref> They are the only representatives of the class Homoiostelea. |
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Solute fossils have an irregularly shaped flattened body covered in calcite plates, and are up to about 10 cm long. The body has two appendages, interpreted as a "feeding arm" at one end, bearing [[tube feet]] at its end, and a "stele" at the other, which may have been used by the animal to propel itself along the sea floor. <ref>Henry Gee '' Before the backbone: views on the origin of the vertebrates'', Springer, 1996 ISBN 0412483009 page 204</ref> |
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==Taxonomy== |
==Taxonomy== |
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They include the unusual [[stylophoran]]s ([[mitrate]]s and [[cornute]]s), Homoiostelea ([[solute (echinoderm)|solute]]s), the Homostelea (cinctans), and the Ctenocystoidea (ctenoid-bearing homalozoans)<ref name=David2000>{{cite journal|last=David|first=Bruno|coauthors=Lefebvre, Bertrand; Mooi, Rich; and Parsley, Ronald|title=Are homalozoans echinoderms? An answer from the extraxial-axial theory|journal=Paleobiol.|year=2000|volume=26|issue=4|pages=529–555|doi=10.1666/0094-8373(2000)026<0529:AHEAAF>2.0.CO;2}}</ref>. |
They include the unusual [[stylophoran]]s ([[mitrate]]s and [[cornute]]s), Homoiostelea ([[solute (echinoderm)|solute]]s), the Homostelea (cinctans), and the Ctenocystoidea (ctenoid-bearing homalozoans)<ref name=David2000>{{cite journal|last=David|first=Bruno|coauthors=Lefebvre, Bertrand; Mooi, Rich; and Parsley, Ronald|title=Are homalozoans echinoderms? An answer from the extraxial-axial theory|journal=Paleobiol.|year=2000|volume=26|issue=4|pages=529–555|doi=10.1666/0094-8373(2000)026<0529:AHEAAF>2.0.CO;2}}</ref>. |
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They have recently been recognised as a [[paraphyletic]] group. The [[Stylophora|stylophorans]] are now classified as a clade of the [[Crinozoa]], whereas the other three are classified as clades of the [[Blastozoa]]<ref name=David2000/>. |
They have recently been recognised as a [[paraphyletic]] group. The [[Stylophora|stylophorans]] are now classified as a clade of the [[Crinozoa]], whereas the other three are classified as clades of the [[Blastozoa]]<ref name=David2000/>. |
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==References== |
==References== |
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{{reflist}} |
{{reflist}} |
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[[Category:Prehistoric invertebrates]] |
[[Category:Prehistoric invertebrates]] |
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Revision as of 03:38, 2 October 2011
| Homalozoa | |
|---|---|
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| Cothurnocystis | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Echinodermata |
| Groups included | |
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The Homalozoa are extinct, Paleozoic echinoderms that lacked the typical pentamer body form. Instead all homalozoans were markedly asymmetric. Homalozoans are extremely variable in forms, but they all were sessile animals. The body (theca) was covered with calcite plates with a number of openings. Their form is in some cases so unusual that it is unclear which openings are to be considered as mouth and anus. Many of them were stalked, similar to sea lilies (crinoids), but often their bodies were bent over, so that the mouth and anus projected forwards rather than upwards. Some forms, especially stylophorans, rested flat on the sea floor[1]. In some forms the single ray (brachiole or aulacophore) possessed an ambulacral groove[2]. It has been claimed that some forms possessed gills and gill slits[3].
Solute
Solutes are an extinct type of invertebrate marine animal, from the Paleozoic era. They are carpoid echinoderms (Homalozoa). Unlike many other types of echinoderm, they lack radial symmetry (such as the five limbs of a starfish). [4] [5] They are the only representatives of the class Homoiostelea.
Solute fossils have an irregularly shaped flattened body covered in calcite plates, and are up to about 10 cm long. The body has two appendages, interpreted as a "feeding arm" at one end, bearing tube feet at its end, and a "stele" at the other, which may have been used by the animal to propel itself along the sea floor. [6]
Taxonomy
Homalozoans were traditionally considered to be stem-group echinoderms[7], but had also been considered to lie in the stem lineage of the chordates (calcichordates). However, it is now generally accepted that homalozoans were echinoderms because their calcite skeleton was composed of the typical stereom crystalline structure[8].
They include the unusual stylophorans (mitrates and cornutes), Homoiostelea (solutes), the Homostelea (cinctans), and the Ctenocystoidea (ctenoid-bearing homalozoans)[9]. They have recently been recognised as a paraphyletic group. The stylophorans are now classified as a clade of the Crinozoa, whereas the other three are classified as clades of the Blastozoa[9].
References
- ^ Lefebvre, Bertrand (2003). "Functional Morphology of Stylophoran Echinoderms". Palaeontology. 46 (3): 511–555. doi:10.1111/1475-4983.00309.
- ^ Barnes, Robert D. (1982). Invertebrate Zoology. Philadelphia, PA: Holt-Saunders International. p. 1011. ISBN 0-03-056747-5.
- ^ Dominguez, Patrício (2002). "Paired gill slits in a fossil with a calcite skeleton". Nature. 417 (6891): 841–844. doi:10.1038/nature00805. PMID 12075349.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ A. B. Smith Deuterostome phylogeny and the interpretation of problematic fossil echinoderms, page 543-544 in Thomas Heinzeller, James H. Nebelsick Echinoderms: München, CRC Press, 2004 ISBN 0415364817,
- ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1002/gj.1018, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with
|doi=10.1002/gj.1018instead. - ^ Henry Gee Before the backbone: views on the origin of the vertebrates, Springer, 1996 ISBN 0412483009 page 204
- ^ James W. Valentine (2004). On the origin of phyla. University Chicago Press. 608 pp. Paperback. ISBN 0226845486..
{{cite book}}: Check|isbn=value: invalid character (help) - pages 401-404 - ^ UCMP Berkely, edu. "Echinodermata: Morphology". University of California Museum of Paleontology. Retrieved 21 March 2011.
- ^ a b David, Bruno (2000). "Are homalozoans echinoderms? An answer from the extraxial-axial theory". Paleobiol. 26 (4): 529–555. doi:10.1666/0094-8373(2000)026<0529:AHEAAF>2.0.CO;2.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help)
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