an echinoderm of the order Spatangoida, having an elongate, somewhat heart-shaped outer covering.
Origin of heart urchin
First recorded in 1835–45
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
any echinoderm of the genus Echinocardium, having a heart-shaped body enclosed in a rigid spiny test: class Echinoidea (sea urchins)
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012