A genus of extinct sea urchins from the Paleozoic era, characterized by relatively circular test bodies and specific arrangements of spines and plates.
From Greek 'kyklos' (circle) + Greek 'tauros' (bull, or round form), a formal Latinized genus name for these circular-bodied extinct echinoderms.
Cyclothurus fossils are found in rocks hundreds of millions of years old, and by studying them, paleontologists learned that sea urchins have remained relatively unchanged in basic body plan since the Paleozoic—true evolutionary survivors.
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