A marine echinoderm which has a spherical or flattened shell covered in mobile spines, with a mouth on the underside and calcareous jaws.
- Class Echinoidea
More example sentences
- The sea urchin is one of the few marine organisms whose genome has been sequenced.
- The inner shell of a sea urchin is a hollow globe, scored in five curved sections that taper at the ends into a small hole at the top and bottom.
- The red sea urchin's body is domed above and flat below.
Definition of sea urchin in:
- The US English dictionary