Sea Urchin

Fascinating facts about the Sea Urchin

• Around 950 sea-urchin species carpet the ocean floor, living on the seabed in every ocean. They occupy all climates, from tropical waters to polar seas, and can be found from the intertidal zone down to the deepest hadal trenches. This worldwide distribution means they inhabit rocky shores, soft sediments and even abyssal plains, thriving wherever benthic habitats exist.
• The biggest sea-urchin species can grow to 36 cm across, dwarfing the typical 3-10 cm individuals that make up most of the class. Their rigid, spherical test bears movable spines that protect the animal while it moves across the substrate.
• Sea urchins chew with a five-toothed, calcium-carbonate lantern surrounded by a fleshy, tongue-like pad that pushes food into the mouth. Five strong, arrow-shaped plates called pyramids form the jaw apparatus, each bearing a hard tooth that can scrape, grasp and tear algae or soft prey. The efficiency of this grinding system has even inspired engineers to model mechanical tools after it.
• Red sea urchins travel far when food is scarce, covering up to 50 cm in a day, but slow to about 7.5 cm when food is abundant. Their locomotion relies on hundreds of tiny tube feet that crawl along the substrate, while the spines can push or lift the body. This speed change is linked to feeding, as the animal moves farther to locate new algae or sessile prey when hunger intensifies.
• Sea urchins build their hard protective test by turning dissolved carbon dioxide into calcium carbonate through a nickel-catalysed reaction. The test is a rigid endoskeleton of fused calcium-carbonate plates that encloses most internal organs. This biochemical conversion continuously adds material as the animal grows, keeping the shell strong and functional throughout its life.

Sources

Every fact above was checked against these pages, and kept only where one of them states it.

• Wikipedia

At a glance

About the Sea Urchin

As the tide recedes, a sea urchin slowly emerges from the shadows, its delicate, lace-like spines swaying gently in the current like a ballet dancer's skirt. With a mesmerizing, almost hypnotic slowness, it inches its way across the rocky substrate, leaving behind a trail of neatly grazed algae and seaweed, a testament to its quiet yet relentless industriousness. In this tranquil, underwater world, the sea urchin is a humble, unassuming monarch, its very stillness a reminder of the beauty that can be found in the most unexpected of creatures.

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