Mitrate
| Mitrate Temporal range:
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Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Echinodermata |
| Class: | †Stylophora |
| Order: | †Mitrata Jaekel, 1918 |
Mitrates are an extinct group of stem group echinoderms, which may be closely related to the hemichordates. Along with the cornutes, they form one half of the Stylophora.
Morphology[edit]
The organisms were a few millimetres long.[1] 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.[2] However, they do not display the familiar fivefold symmetry that more recent echinoderms possess, instead being close to (but not fully) bilaterally symmetrical.[1][3]
Their heads had two sides; one, flat, was covered with large "pavement-like"[1] plates, the other, convex, bore smaller plates.[1] Their tails were long and segmented, resembling the stalk of a crinoid or the arm of a brittlestar.[1] At the opposite end was a hole which may have been mouth or anus - or both.[1]
They also bear features reminiscent of pharyngeal slits,[4] a character lost in other echinoderms but present in hemichordates,[1] causing R.P.S. Jefferies to hold them as the ancestor of all chordates.
Behaviour[edit]
Mitrates^ have been found with associated trace fossils.[5][6] 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.[1] The trace fossils suggest that they pulled themselves through the mud with their "tail", and were flat-side up.[1]
Notes[edit]
^ Rhenocystis latipedunculata
References[edit]
- ^ a b c d e f g h i j Gee, H. (2000). "Mitrates on the move". Nature. 407 (6806): 849–851. doi:10.1038/35038193. PMID 11057650.
- ^ Lefebvre, Bertrand; Guensburg, Thomas E.; Martin, Emmanuel L. O.; Mooi, Rich; Nardin, Elise; Nohejlová, Martina; Saleh, Farid; Kouraïss, Khaoula; El Hariri, Khadija (2019-02-01). "Exceptionally preserved soft parts in fossils from the Lower Ordovician of Morocco clarify stylophoran affinities within basal deuterostomes". Geobios. 52: 27–36. doi:10.1016/j.geobios.2018.11.001. ISSN 0016-6995.
- ^ "Palaeos Metazoa: Deuterostomia: Stylophora". Retrieved 2023-03-04.
- ^ Jefferies, R.P.S. (1986). The Ancestry of the Vertebrates. British Museum (Natural History).
- ^ Sutcliffe, O.E.; Südkamp, W.H.; Jefferies, R.P.S. (2000). "Ichnological evidence on the behaviour of mitrates: two trails associated with the Devonian mitrate Rhenocystis". Lethaia. 33 (1): 1–12. doi:10.1080/00241160050150267.
- ^ Rahman, I.A.; Jefferies, R.P.S.; Südkamp, W.H.; Smith, R.D.A. (2009). "Ichnological insights into mitrate palaeobiology". Palaeontology. 52 (1): 127–138. doi:10.1111/j.1475-4983.2008.00838.x.
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