A sea urchin is a round sea creature covered in sharp spines. Stand on a sea urchin.
It walks on hundreds of tiny tube feet and grazes algae off rock. The spines break off in a foot and are best left to dissolve rather than dug out.
1nounsea urchinA round sea creature covered in sharp spines.
“He trod on a sea urchin and limped for a fortnight.”
sea urchin is a creature.
Sea plus urchin, an old word for a hedgehog.
From sea + urchin, reflecting a similarity in appearance to a hedgehog.
Etymology from Wiktionary, CC BY-SA
Practised in Insects & Sea Life