Mitrate
| Mitrate Temporal range:
| |
|---|---|
| Error creating thumbnail: | |
| Enoploura balanoides | |
| Scientific classification Edit this classification | |
| 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 | edit source]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 | edit source]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 | edit source]^ Rhenocystis latipedunculata
References
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