Mitrate

{{Short description|Extinct order of marine invertebrates}} {{Automatic taxobox | fossil_range = Cambrian (Guzhangian)–Carboniferous (Morrowan)<ref>{{Cite PBDB|taxon|31183|Mitrata}}</ref> {{Geological range|Guzhangian|318.6|}} | taxon = Mitrata | image = Rhenocystis latipedunculata.png | image_caption = ''Rhenocystis latipedunculata'' ventral/flat (B1) and dorsal/convex (B2) surfaces | authority = Jaekel, 1918 | subdivision_ranks = Taxa | subdivision = See Taxa }}

'''Mitrates''' are an extinct group of echinoderms, which are grouped with the cornutes and the basal ''Ceratocystis'' to form the Stylophora. Mitrates were central to the now-disproven<ref name=Boisset2024>{{cite journal|last1=Boisset |first1=Thomas |last2=Lefebvre |first2=Bertrand |last3=Mooi |first3=Rich |last4=Kroh |first4=Andreas |last5=Winkler |first5=Viola |last6=Adrien |first6=Jérôme |last7=Martin |first7=Markus J. |year=2024 |title=Insights into stylophoran anatomy and taphonomy based on an exceptionally preserved mitrate from the Lorraine Group (Upper Ordovician) of New York, USA |journal=Cah. Biol. Mar. |volume=65 |pages=511–516 |doi=10.21411/CBM.A.33CFD1AB}}</ref> calcichordate hypothesis of chordate origins, but are now seen as either pre-radial-symmetry stem-group echinoderms,<ref>{{cite journal|last1=Rahman |first1=Imran A. |last2=Zamora |first2=Samuel |date=July 2024 |title=Origin and early evolution of echinoderms |journal=Annual Review of Earth and Planetary Sciences |volume=52 |pages=295–320 |issue=1 |doi=10.1146/annurev-earth-031621-113343|bibcode=2024AREPS..52..295R |hdl=10141/623070 |url=http://zaguan.unizar.es/record/145576 |hdl-access=free }}</ref> or as a derived group either within the blastozoans<ref>{{cite journal|last1=Mooi |first1=Rich |last2=Lefebvre |first2=Bertrand |last3=Guensburg |first3=Thomas E. |last4=Nohejovlá |first4=Martina |last5=Dupichaud |first5=Christophe |date=December 2024 |title=Approaches to understanding echinoderm origins. Part 2: Questioning conceptual models |journal=Cahiers de Biologie Marine |volume=65 |pages=463–490 |doi=10.21411/CBM.A.604F2876}}</ref> or near to the origin of crinoids.<ref>{{cite journal|last1=Guensburg |first1=Thomas E. |last2=Sprinkle |first2=James |last3=Mooi |first3=Rich |last4=Lefebvre |first4=Bertrand |last5=David |first5=Bruno |last6=Roux |first6=Michel |last7=Derstler |first7=Kraig |year=2020 |title=Athenacrinus n. gen. and other early echinoderm taxa inform crinoid origin and arm evolution |journal=Journal of Paleontology |volume=94 |number=2 |pages=311–333 |doi=10.1017/jpa.2019.87}}</ref>

==Morphology== The organisms were a few millimetres long.<ref name=Gee2000/> Like the echinoderms, they are covered in armour plates, each of which comprises a single crystal of calcite. This is one of the features they share with the latter group, along with a water vascular system, only discovered in 2019.<ref>{{Cite journal |last1=Lefebvre |first1=Bertrand |last2=Guensburg |first2=Thomas E. |last3=Martin |first3=Emmanuel L. O. |last4=Mooi |first4=Rich |last5=Nardin |first5=Elise |last6=Nohejlová |first6=Martina |last7=Saleh |first7=Farid |last8=Kouraïss |first8=Khaoula |last9=El Hariri |first9=Khadija |date=2019-02-01 |title=Exceptionally preserved soft parts in fossils from the Lower Ordovician of Morocco clarify stylophoran affinities within basal deuterostomes |journal=Geobios |volume=52 |pages=27–36 |doi=10.1016/j.geobios.2018.11.001 |issn=0016-6995 |doi-access=free |bibcode=2019Geobi..52...27L }}</ref> However, they do not display the familiar fivefold symmetry that more recent echinoderms possess, instead being close to (but not fully) bilaterally symmetrical.<ref name=Gee2000/><ref>{{cite web |url=http://palaeos.com/metazoa/deuterostomia/homalozoa/stylophora.html |title=Palaeos Metazoa: Deuterostomia: Stylophora |access-date=2023-03-04}}</ref>

Their heads had two sides; one, flat, was covered with large "pavement-like"<ref name=Gee2000/> plates, the other, convex, bore smaller plates.<ref name=Gee2000/> Their tails were long and segmented, resembling the stalk of a crinoid or the arm of a brittlestar.<ref name=Gee2000/> At the opposite end was a hole which may have been mouth or anus - or both.<ref name=Gee2000/>

They also bear features reminiscent of pharyngeal slits,<ref name=Jefferies1986>{{cite book |author = Jefferies, R. P. S. |year = 1986 |title = The Ancestry of the Vertebrates |publisher = British Museum (Natural History) |isbn =}}</ref> a character lost in other echinoderms but present in hemichordates.<ref name=Gee2000/> This caused R. P. S. Jefferies to hold them as the ancestor of all chordates, a theory that has since been disproven.<ref name=Boisset2024 />

==Behaviour==

The mitrate ''Rhenocystis latipedunculata'' has been found with associated trace fossils.<ref name=Sutcliffe2000>{{Cite journal |last=Sutcliffe |first=Owen E. |last2=Südkamp |first2=Wouter H. |last3=Jefferies |first3=Richard P. S. |date=March 2000 |title=Ichnological evidence on the behaviour of mitrates: two trails associated with the Devonian mitrate Rhenocystis |url=https://www.scup.com/doi/10.1080/00241160050150267 |journal=Lethaia |language=en |volume=33 |issue=1 |pages=1–12 |doi=10.1080/00241160050150267 |issn=0024-1164}}</ref><ref name=Rahman2009>{{Cite journal |last=Rahman |first=Imran A. |last2=Jefferies |first2=Richard P. S. |last3=SüDkamp |first3=Wouter H. |last4=Smith |first4=Ru D. A. |date=January 2009 |title=Ichnological insights into mitrate palaeobiology |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1475-4983.2008.00838.x |journal=Palaeontology |language=en |volume=52 |issue=1 |pages=127–138 |doi=10.1111/j.1475-4983.2008.00838.x |issn=0031-0239}}</ref> Their interpretation requires an understanding of how the animal was oriented in life; it's not agreed whether the convex side of the head was up or down, or indeed whether the "tail" was at the front or back of the organism.<ref name=Gee2000>{{Cite journal |last=Gee |first=Henry |date=October 2000 |title=Mitrates on the move |url=https://www.nature.com/articles/35038193 |journal=Nature |language=en |volume=407 |issue=6806 |pages=849–851 |doi=10.1038/35038193 |issn=0028-0836}}</ref> The trace fossils suggest that they pulled themselves through the mud with their "tail", and were flat-side up.<ref name=Gee2000/>

== Taxa == The following taxa are recognized as being included in the Mitrata as of a 2002 review of the order:<ref name=Dominguez_et_al2002>{{Cite journal |last=Domínguez Alonso |first=Patricio |last2=Jefferies |first2=Richard P. S. |last3=Gil Cid |first3=María Dolores |date=December 2002 |title=An annotated check-list of genera and species of carpoids |url=https://hdl.handle.net/20.500.14352/56880 |journal=Coloquios de Palcontologia |volume=53 |pages=33-68 |issn=1132-1660}}</ref>

{{div col|colwidth=25em|small=yes}} *''Adoketocarpus'' {{Small|Ruta & Jell, 1999}} *''Allanicytidium'' {{Small|Caster & Gill, 1967}} *''Anatifopsis'' {{Small|Barrande, 1872}} *''Anomalocystites'' {{Small|Hall, 1859}} *''Aspidocarpus'' {{Small|Ubaghs, 1979}} *''Ateleocystites'' {{Small|Billings, 1858}} *''Australocystis'' {{Small|Caster, 1954}} *''Balanocystites'' {{Small|Barrande, 1887}} *''Barrandeocarpus'' {{Small|Ubaghs, 1979}} *''Bokkeveldia'' {{Small|Ruta & Theron, 1997}} *''Chauvelia'' {{Small|Cripps, 1990}} *''Chinianocarpos'' {{Small|Ubaghs, 1961}} *''Dalejocystis'' {{Small|Prokop, 1963}} *''Diamphidiocystis'' {{Small|Kolata & Guensburg, 1979}} *''Enoploura'' {{Small|Wetherby, 1879}} *''Eumitrocystella'' {{Small|Beisswenger, 1994}} *''Guichenocarpos'' {{Small|Chauvel, 1981}} *''Jaekelocarpus'' {{Small|Kolata, Frest & Mapes, 1991}} *''Kierocystis'' {{Small|Parsley, 1991}} *''Kopficystis'' {{Small|Parsley, 1991}} *''Lagynocystis'' {{Small|Jaekel, 1918}} *''Milonicystis'' {{Small|Chauvel, 1986}} *''Mitrocystella'' {{Small|Jaekel, 1901}} *''Mitrocystites'' {{Small|Barrande, 1887}} *''Mongolocarpos'' {{Small|Rozhnov, 1990}} *''Notocarpos'' {{Small|Philip, 1981}} *''Occultocystis'' {{Small|Haude, 1995}} *''Ovocarpus'' {{Small|Ubaghs, 1994}} *''Paranacystis'' {{Small|Caster, 1954}} *''Peltocystis'' {{Small|Thoral, 1935}} *''Placocystella'' {{Small|Rennie, 1936}} *''Placocystites'' {{Small|de Koninck, 1869}} *''Protocytidium'' {{Small|Ruta & Jell, 1999}} *''Pseudovictoriacystis'' {{Small|Ruta & Jell, 1999}} *''Rhenocystis'' {{Small|Dehm, 1932}} *''Spermacystis'' {{Small|Ubaghs, 1967}} *''Tasmanicytidium'' {{Small|Caster, 1983}} *''Victoriacystis'' {{Small|Gill & Caster, 1960}} *''Vizcainocarpus'' {{Small|Ruta, 1997}} *''Willmanocystis'' {{Small|Kolata & Jollie, 1982}} *''Yachalicystis'' {{Small|Haude, 1995}} {{div col end}}

==References== {{Reflist}}

Category:Homalozoa