Resembling a hedgehog or sea urchin; a member of the class Echinoidea, which includes sea urchins and sand dollars.
From Greek echinos (hedgehog) + -oid (resembling), used since the 1800s to classify the spiny spherical marine animals we call sea urchins.
Sea urchins have been around for 250 million years, and their spherical spiky design is so efficient that military engineers study their structure to design better armor.
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