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Somasteroidea
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Somasteroidea

fossil echinoderm class
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The Somasteroidea were an extinct class of echinoderms that existed from the Lower Ordovician to the Upper Devonian periods, approximately 350 to 500 million years ago. These marine invertebrates superficially resembled modern starfishes (Asteroidea) but lacked the characteristic groove for tube feet. Echinoderms, as a phylum, are characterized by a spiny skin and a five-part body symmetry, with a rich fossil history dating back to the Cambrian Period. The classification of echinoderms is primarily based on skeletal structures, with many extinct classes known only from fossils.12

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  1. echinoderm - Annotated classification
  2. echinoderm

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