Mitrate

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. 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.[1]

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,[2] 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.

Mitrates^ have been found with associated trace fossils.[3][4] 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]

^ Rhenocystis latipedunculata