Sea urchins point the way

LH Sweat, Smithsonian Marine Station at Fort Pierce

Arbacia punctulata, the purple-spined sea urchin, is native to the western Atlantic Ocean along the eastern coast of the US and the Gulf of Mexico, where it usually lives on rock or shell substrates. It is spherical in shape and bristled with long, slender, dark purple spines, which are shorter on the lower aspect of the urchin, surrounding the oral apparatus. The test, or shell, of the urchin can reach 3–5 cm in diameter and has holes through which the urchin’s tube feet extend. It uses its spines and tube feet for locomotion. A. punctulata is primarily herbivorous, consuming algae and other organisms that grow on the rocks around it using a specialized structure called Aristotle’s lantern, which is comprised of five hard plates that move together like a beak, to scrape food off the rocks.

Lab Anim. (NY) 43, 263 (2014).
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