Do Sea Urchins Have Teeth? The Surprising Truth

Sea urchins are marine invertebrates that are members of the class Echinoidea. They are commonly called echinoderms, a term which essentially means “spiky skin.” Found in all of the world’s oceans, there are around 1,000 species. They live on the sea floor, especially in rocky areas. Sea urchins have a regular, spherical body shape and an internal skeleton called a “test.” They are opportunistic omnivores and primarily eat algae, but they also consume small invertebrates like mussels, barnacles, and sponges, as well as organic debris. So, do sea urchins have teeth? Keep reading to discover the surprising truth.

Do Sea Urchins Actually Have Teeth?

The mouth of a sea urchin is situated on its underside. Most sea urchins have five, chisel-shaped teeth set in a radial jaw. This feeding apparatus is called Aristotle’s lantern, a name given by Aristotle because it resembles a lantern with five panes.

Sea urchin teeth are primarily composed of calcium carbonate (CaCO₃) crystals. They are also self-sharpening, replacing material that has become worn down due to abrasion. The teeth are structured as long shafts made up of tiny, densely packed plates and fibers bonded together by calcite. The plates chip off when they become worn, leaving a freshly-sharpened tip. To compensate for the loss of material, sea urchin teeth grow continuously throughout their lives.

How Do Sea Urchins Eat?

Their strong, sharp teeth allow sea urchins to scrape and grind holes into rocks. They scrape algae off rocks or consume detritus from the sea floor. As they eat, they make channels or grooves in the stone. As the urchin chews, it removes pieces of the rock along with the algae. However, algae rapidly reproduces on exposed surfaces. By making these depressions in the rock, the urchin not only creates a hiding place but also gets nutrition from the algae growing inside its shelter.

Sea urchins move using hundreds of tube feet that typically have suction cups at the tips. Hydraulic pressure pumps water into and out of the tubes when their muscles contract and relax, which extends the feet outward and retracts them. They generally use their feet to hold on to surfaces while feeding, but they can use their spines, and even their teeth, to push themselves along the ocean floor. If something edible lands on a sea urchin’s body, it uses its tube feet to grasp it and bring the food to its mouth.

Do Sea Urchins Bite?

Sea urchins do not bite in the way humans understand biting. A sea urchin’s teeth could scrape skin, but as their teeth are on their undersides, it is unlikely. Most injuries from sea urchins are puncture wounds from stepping on them or brushing up against them.

Among their spines, some sea urchins, such as the collector sea urchin, have tubular stalks with biting, jaw-like structures called pedicellariae. The pedicellariae have three jaws and pincer-like heads, releasing venom as they attack predators. Sea urchin stings can be very painful, especially if the punctures are deep or if you are stung by pedicellariae.