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Mitrates are an extinct group of stem group Echinoderms, which may be closely related to the hemichordates. ==Morphology== The organisms were a few millimetres long.〔 Like the echinoderms, they are covered in armour plates, each of which comprises a single crystal of calcite. However, this is arguably the only feature they share with the latter group; they don't have, for example, fivefold symmetry or a water vascular system.〔 Their heads had two sides; one, flat, was covered with large "pavement-like"〔 plates, the other, convex, bore smaller plates.〔 Their tails were long and segmented, resembling the stalk of a crinoid or the arm of a brittlestar.〔 At the opposite end was a hole which may have been mouth or anus - or both.〔 They also bear features reminiscent of pharyngeal slits, a character lost in echinoderms but present in hemichordates,〔 causing R.P.S. Jefferies to hold them as the ancestor of all chordates. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「mitrate」の詳細全文を読む スポンサード リンク
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