sea urchin n. Any of various echinoderms of the class Echinoidea, having a soft body enclosed in a rounded, radially symmetrical, calcareous skeleton covered with long spines. sea urchin n (Animals) any echinoderm of the class Echinoidea, such as Echinus esculentus (edible sea urchin), typically having a globular body enclosed in a rigid spiny test and …



