The Homalozoa lacked the typical pentamer body form of other echinoderms, but all were sessile animals. Instead all Homalozoans were markedly asymmetric, and were extremely variable in forms.
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.[2]
In some forms the single ray (brachiole or aulacophore) possessed an ambulacral groove.[3]
Homalozoans were traditionally considered to be stem-group echinoderms,[5] 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.[6]
They include the unusual stylophorans (mitrates and cornutes), Homoiostelea (solutes), the Homostelea (cinctans), and the Ctenocystoidea (ctenoid-bearing homalozoans).[7] They have recently been recognised as a polyphyletic group. The stylophorans are now classified as a clade of the Crinozoa, whereas the other three are classified as clades of the Blastozoa.[7]
Solutesedit
Unlike many other types of echinoderm, solute homalozoans lack radial symmetry (such as the five limbs of a starfish).[8][9] Solutes are the sole order 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.[10]
^Barnes, Robert D. (1982). Invertebrate Zoology. Philadelphia, PA: Holt-Saunders International. p. 1011. ISBN978-0-03-056747-6.
^Dominguez, Patrício; Jacobson, Antone G.; Jefferies, Richard P. S. (2002). "Paired gill slits in a fossil with a calcite skeleton". Nature. 417 (6891): 841–844. Bibcode:2002Natur.417..841D. doi:10.1038/nature00805. PMID 12075349.
^James W. Valentine (2004). On the origin of phyla. University Chicago Press. 608 pp. Paperback. ISBN978-0-226-84548-7. - pages 401-404
^UCMP Berkeley, edu. "Echinodermata: Morphology". University of California Museum of Paleontology. Retrieved 21 March 2011.
^ abDavid, Bruno; Lefebvre, Bertrand; Mooi, Rich; Parsley, Ronald (2000). "Are homalozoans echinoderms? An answer from the extraxial-axial theory". Paleobiology. 26 (4): 529–555. doi:10.1666/0094-8373(2000)026<0529:AHEAAF>2.0.CO;2.
^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 ISBN0-415-36481-7,
^Smith, A. B. (2005). "The pre-radial history of echinoderms". Geological Journal. 40 (3): 255–280. doi:10.1002/gj.1018.
^Henry Gee Before the backbone: views on the origin of the vertebrates, Springer, 1996 ISBN0-412-48300-9 page 204
April 12, 2024
homalozoa, obsolete, extinct, subphylum, paleozoic, echinoderms, prehistoric, marine, invertebrates, they, also, referred, carpoids, cothurnocystis, paleozoic, scientific, classificationdomain, eukaryotakingdom, animaliaphylum, echinodermatasubphylum, whitehou. Homalozoa is an obsolete extinct subphylum of Paleozoic era echinoderms prehistoric marine invertebrates They are also referred to as carpoids 1 HomalozoaCothurnocystis Paleozoic era Scientific classificationDomain EukaryotaKingdom AnimaliaPhylum EchinodermataSubphylum HomalozoaWhitehouse 1941Groups includedStylophora mitrates and cornutes Soluta Cincta Ctenocystoidea ctenoid bearing homalozoans Contents 1 Description 2 Taxonomy 2 1 Solutes 3 See also 4 ReferencesDescription editThe Homalozoa lacked the typical pentamer body form of other echinoderms but all were sessile animals Instead all Homalozoans were markedly asymmetric and were extremely variable in forms 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 2 In some forms the single ray brachiole or aulacophore possessed an ambulacral groove 3 It has been claimed that some forms possessed gills and gill slits 4 Taxonomy editHomalozoans were traditionally considered to be stem group echinoderms 5 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 6 They include the unusual stylophorans mitrates and cornutes Homoiostelea solutes the Homostelea cinctans and the Ctenocystoidea ctenoid bearing homalozoans 7 They have recently been recognised as a polyphyletic group The stylophorans are now classified as a clade of the Crinozoa whereas the other three are classified as clades of the Blastozoa 7 Solutes edit Unlike many other types of echinoderm solute homalozoans lack radial symmetry such as the five limbs of a starfish 8 9 Solutes are the sole order 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 10 See also editPrehistoric echinoderms Blastozoa Cystoidea Paleozoic echinodermsReferences edit Imran Rahman January February 2009 Making sense of carpoids Geology Today 25 1 34 38 doi 10 1111 j 1365 2451 2009 00703 x 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 978 0 03 056747 6 Dominguez Patricio Jacobson Antone G Jefferies Richard P S 2002 Paired gill slits in a fossil with a calcite skeleton Nature 417 6891 841 844 Bibcode 2002Natur 417 841D doi 10 1038 nature00805 PMID 12075349 James W Valentine 2004 On the origin of phyla University Chicago Press 608 pp Paperback ISBN 978 0 226 84548 7 pages 401 404 UCMP Berkeley edu Echinodermata Morphology University of California Museum of Paleontology Retrieved 21 March 2011 a b David Bruno Lefebvre Bertrand Mooi Rich Parsley Ronald 2000 Are homalozoans echinoderms An answer from the extraxial axial theory Paleobiology 26 4 529 555 doi 10 1666 0094 8373 2000 026 lt 0529 AHEAAF gt 2 0 CO 2 A B Smith Deuterostome phylogeny and the interpretation of problematic fossil echinoderms page 543 544 in Thomas Heinzeller James H Nebelsick Echinoderms Munchen CRC Press 2004 ISBN 0 415 36481 7 Smith A B 2005 The pre radial history of echinoderms Geological Journal 40 3 255 280 doi 10 1002 gj 1018 Henry Gee Before the backbone views on the origin of the vertebrates Springer 1996 ISBN 0 412 48300 9 page 204 Retrieved from https en wikipedia org w index php title Homalozoa amp oldid 1202741475, wikipedia, wiki, book, books, library,
