Gill & Caster, 1960
The stylophorans are an extinct, possibly polyphyletic group allied to the Paleozoic Era echinoderms, comprising the prehistoric cornutes and mitrates. It is synonymous with the subphylum Calcichordata.
The general stylophoran body plan consists of a flattened theca and a single jointed appendage which extends from it. Stylophoran tests are composed of stereom calcite plates like an echinoderm, which has traditionally been the basis for assigning them to Echinodermata. However, they also lack the radial symmetry characteristic of most other echinoderms, with the earlier members of the group being flattened and asymmetrical, and the later ones closer to bilateral symmetry.
In Mitrocystites and perhaps in other forms its stem does not end in an attachment organ, and the stem more likely served the organism as a tail for movement. Cothurnocystis is asymmetrical and boot-shaped, and Mitrocystites is bilaterally symmetrical and more streamlined.
This reconstruction leads to the alternative hypothesis that some or all of the stylophorans may have been ancestral to the chordate branch of the deuterostomes, rather than being within the echinoderms.
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