The term "sea-hedgehog" refers to a type of sea urchin with spines that resemble those of a hedgehog. There are several synonyms for this unique marine organism, including the names "sea-urchin," "urchin," and "sea-egg." These synonyms allude to the hard, spherical shape of the creature and its spiny exterior. "Sea-urchin" and "sea-egg" are most commonly used, as these terms are more familiar to those who are not familiar with the term "sea-hedgehog." Regardless of the term used, these creatures are fascinating and important parts of their marine ecosystems, contributing to the balance and diversity of life in our oceans.