Dictionary.com
Thesaurus.com

heart urchin

American  

noun

  1. an echinoderm of the order Spatangoida, having an elongate, somewhat heart-shaped outer covering.


heart urchin British  

noun

  1. 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

Etymology

Origin of heart urchin

First recorded in 1835–45

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

According to the Cornwall Wildlife Trust, the sea potato, which is also known as a heart urchin, lives buried in up to 15cm of sand or muddy sediment.

From BBC

The nocturnal sea mouse, four centimeters long, is a kind of heart urchin with thin spines that can hurt a diver digging in the sand for it. 

From New York Times