Cyclocystoidea

fossil echinoderm class

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June 25, 2026

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The Cyclocystoidea were an extinct class of primitive echinoderms that existed from the Middle Ordovician to the Late Devonian periods. These marine invertebrates were characterized by saclike bodies attached to a stem anchored to the seafloor, with their bodies covered in numerous plates. Some species of Cyclocystoidea are considered important index fossils, aiding in the correlation of rock units. They are classified within the subphylum Echinozoa.12

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echinoderm
Annotated classification
†Class Cyclocystoidea Middle Ordovician to Middle Devonian about 375,000,000–460,000,000 years ago; small, disk-shaped; theca composed of numerous plates; ambulacral system with multiple branching. †Class Edrioasteroidea Lower Cambrian to Lower Carboniferous about 340,000,000–570,000,000 years ago; discoid to cylindrical; 5 well-developed straight or
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†Class Cyclocystoidea Middle Ordovician to Middle Devonian about 375,000,000–460,000,000 years ago; small, disk-shaped; theca composed of numerous plates; ambulacral system with multiple branching. †Class Edrioasteroidea Lower Cambrian to Lower Carboniferous about 340,000,000–570,000,000 years ago; discoid to cylindrical; 5 well-developed straight or
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