Megabalanus coccopoma, the titan acorn barnacle, is a tropical species of barnacle first described by Charles Darwin in 1854. Its native range is the Pacific coasts of South and Central America but it is extending its range to other parts of the world. Size of each  calcareous cone : roughly 30 millimetres in both diameter and height.
<a href="//commons.wikimedia.org/wiki/User:Marina_Karaevangelou" title="User:Marina Karaevangelou">Marina Karaevangelou</a>
CC BY-SA 4.0
<span class="int-own-work" lang="en">Own work</span>