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Sea Life, Animals
& Exhibits

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Pencil Sea Urchin

(Eucidaris tribuloides)

Tan to dark reddish-brown in color, the pencil urchin has distinct thick, blunt spines that move in any direction. The spines are often coated with sponges or coralline algae. Pencil urchins have five similar parts that make up their test(body), or rigid skeleton, called pentamerous radial symmetry. These are five skeletal plates that equally cover their body.

Aristotle’s description of the sea urchin mouth, is the reason why it is termed as ‘Aristotle’s lantern’.


Pencil urchins are found in the Western Atlantic coastal areas from South Carolina to Florida and the Caribbean, as well as the eastern coast of Mexico to Brazil. Found in shallow waters, including coral reefs and rocky-bottomed areas near the low tide line and below.


Although primarily herbivorous, pencil urchins are opportunistic feeders and will scavenge for other types of food. They generally come out at night to feed, moving around and using their hard, horned teeth to scrape algae and other plant matter off rocks and corals. However, they’ll also eat sponges, barnacles, mussels and dead fish or other sea creatures.


Despite males and females looking exactly alike, pencil urchins have distinct and separate sexes. They reproduce using external fertilization. Females release eggs and males release sperm into the water simultaneously, where they will join and become fertilized. Females can produce thousands, or even millions, of eggs in one go. Once hatched, these tiny urchins start out their lives as larvae and take roughly two years to reach their full adult size.


Predators of sea urchins are triggerfish and large wrasses, who nibble away at their spines before turning them over to eat the fleshy undersides.