Test ("shell") of a sea urchin,  <i><a href="//commons.wikimedia.org/wiki/Category:Echinometra_mathaei" title="Category:Echinometra mathaei">Echinometra mathaei</a></i>, from Maldives (Ari atoll).
<a href="//commons.wikimedia.org/wiki/User:FredD" title="User:FredD">Frédéric Ducarme</a>
CC BY-SA 4.0
<span class="int-own-work" lang="en">Own work</span>