15 Cool Sea Urchin Facts You Should Know

Sea urchin is a type of marine animal that mostly lives in shallow ocean waters, and it is also known as “sea hedgehog”. Sea urchin is one of the most common and major predators in the ocean. Sea urchin is usually yellowish or orange, with parts bearing different colors due to spines on its body. Despite its appearance, the flesh of sea urchin is often sweet, although you might think it tastes bad because of its dark color. Although it’s a typical Japanese food, it is also eaten in other countries like France and Spain. It’s also an ingredient used in various dishes from home cooking to desserts and salads.

If you are a sea marine enthusiast or simply love sea urchin delicacies, you may have high curiosity about this animal. Let’s take a look at some cool sea urchin facts in this article to answer your unanswered question about this animal. From its unique habits to more trivia sea urchin facts, we are sure those revealing facts below will broaden your knowledge. Let’s jump to the list!

1. They Live in All 5 Oceans

Sea urchins are saltwater dwellers, never found in bodies of freshwater. Various species of urchins live in all oceans throughout the world, though they are more abundant in warmer climates. The Atlantic Ocean in the Caribbean, the Pacific Ocean near the Hawaiian Islands, and both the Indian and Pacific Oceans off the coast of Australia are the world’s oceans with the highest concentrations of sea urchins.

In actuality, sea urchins can survive in cold or warm water. Some of them make their homes in the deep, stony seabeds, while some species choose to live in the shallows, on coral reefs, or among kelp forests.

2. They Don’t Have Bones In Their Symmetry Body

Here’s more sea urchin facts you should know: Although you find sea urchins usually have strong spike shells, they actually have no bones. The test, or hard outer shell of sea urchins, is composed of calcium carbonate. However, they lack bone structure. The test is composed of tiny plate segments that completely encircle the sea urchin.

The calcium-filled spines on sea urchins serve as a warning to potential predators. Sea urchins are unquestionably top of the list when it comes to symmetry. They feature what is known as radial symmetry in their bodies. Five equal pieces can be taken from each sea urchin. While they are all coated in protective spines, it may be difficult to discern this symmetry, but when examining a dried urchin shell or test, it is clear to see.

3. Sea Urchin Consume Animals and Plants

When it comes to what they eat, sea urchins are not particularly choosy. They consume both plants and animals since they are omnivores. They eat algae off the corals as their primary food source, although some species also eat mussels, barnacles, marine sponges, and even dead fish. Depending on where they dwell and what’s accessible, sea urchins eat different things. They move along fairly easily.

Furthermore, Aristotle’s Lantern, a unique type of mouth seen on sea urchins, makes it simpler for them to scrape organisms off of surfaces they are traveling over. In this mouth, there are only five teeth, and each one has its own jaw, allowing for easier movement.

4. Sea Urchin’s Spines For Self Protection

The calcium-filled spines on sea urchins serve as a warning to potential predators. They feature long, sharp spines and claw-like projections all over their bodies. Those predators who ignore the warning risk developing spines in their skin. The majority of sea urchin stings resemble being poked by a huge nail or other sharp object.

In reality, otters, birds, fish, crabs, and even humans are among the sea urchins’ many foes. It might be challenging to remove the calcium-filled spines that a sting can leave behind from human skin. However, prompt removal of these can limit additional damage.

5. They Love To Reproduce In Summer

Every summer, countless numbers of people travel to the shore to enjoy the sun and surf. However, they are not alone. Hundreds of millions of tiny sea urchin larvae are also drifting around just beyond the thundering surf, getting ready for one of the animal kingdom’s most spectacular changes. Millions of jelly-coated eggs are released by the mother sea urchins, who use their spines to cling on to the eggs while keeping them close. 

Furthermore, these eggs undergo external fertilization. A swimming embryo develops in less than a day and swims freely until it matures into a juvenile and sinks to the bottom of the sea. Within five years, these sea urchin young reach adulthood. After that, the majority of sea urchins live long lives of up to 30 years.

6. Sea Urchins Can See Without Eyes

More cool sea urchin facts you may never know: although they don’t have eyes, they actually still can “see”.They see using their tube-like tentacle feet instead. Despite hiding their eyes among the spikes, they are nevertheless sensitive to light. Moreover, they possess several genes related to eyes in their feet.

Moreover, the only animals that have been demonstrated to see without eyes are sea urchins. Like the retina of an eye, light-sensitive cells actually cover their entire body. They are particularly prevalent in the sea urchins’ feet, spines, and mouths. Surprisingly, though, sea urchins deliberately avoid light sources because they don’t enjoy it.

7. Sea Urchins Have Hundreds of Feet To Move

A sea urchin appears to be moving by simply bouncing along with the water or by using its spines at first glance. They actually possess tiny, incredibly flexible limbs called tube feet that let them swiftly glide into and out of their shells. With their numerous tube feet, sea urchins can explore their surroundings and cling to the substrate. These tube feet are what are known as hydrostatic skeletons, which are hollow structures that are controlled by the interaction of a muscle envelope and internal fluid pressure.

They propel the rest of their bodies along the seabed with the help of the tube feet that pump air into and out of their bodies. It’s hardly surprising that people frequently confuse a sea urchin’s tube feet and spines because they resemble one another so closely. This gives the impression that a sea urchin moves by using its spines.

8. They Have Simple Nervous System

Here are more surprising sea urchin facts: they don’t actually have brains; instead, a neural ring around their lips serves as the nerve center for their entire body. They have five primary nerves that carry water through, into, and out of their bodies in accordance with their water vascular systems.

From those five nerves, all of their other nerves branch off, going to the sea urchin’s mouth, spine, and tube feet. This gives the sea urchin a sensation of touch and the ability to control its limbs and other vital body components. In addition, they have tiny organs called speridia that are situated near to their main nerves. Given that sea urchins often have spherical bodies, these organs provide them with a sense of gravitational direction, which is crucial for balance.

9. The Most Dangerous Sea Urchin In The World

Flower sea urchin or also known as Toxopneustes pileolus derives its name from the fact that it resembles a flower. The name may sound harmless, but actually it holds the world’s most dangerous sea urchin. It is typically found in the Indian and West Pacific Oceans. The flower urchin is different from other sea urchins in that its spines are small and blunt, but it doesn’t make it any less hazardous. 

However, the two types of poison the flower urchin has put people in peril. The first, albeit it targets the blood and nerves, is not particularly harmful by itself. The second venom, on the other hand, acts to increase the poisonousness of the first venom because it is not toxic on its own. It is capable of causing anaphylactic shock, which can result in death.

10. Sea Urchin Can Regenerate Its Lost Spines

Yes, the bodily components of sea urchins may regrow. They are made of a single crystal from the base to the needle-sharp tip, and when broken off, they regrow quickly. Spine regeneration might take as little as two weeks. This is actually a new finding which was found in 2020 by scientist Max Wisshak.

According to Syfy, Max Wisshak and his team of scientists recently filmed, for the first time ever, a sea urchin trying to regenerate. It had lost a third of its shell and several vital organs, but still crawled for at least 43 more hours, even evading a hungry giant crab. How this echinoderm could still manage to crawl after what it had been through was surreal.

11. Sea Urchin Can Be Environment Indicator

Based on a study published by Journal of Tropical Life Science, sea urchins can serve as a good indication of the state of the ocean environment, particularly the coral reef ecosystem. By eating algae and giving corals a place to settle, urchins help reefs remain resilient. They maintain the conditions required for coral ecosystems to rebound from severe disturbances.

In addition, when the sea urchin population grows out of control due to overfishing and hunting by natural predators, they may devastate the environment. Sea urchins destroy the local algae population, resulting in what scientists call urchin barrens. The name can become misleading, though, as an urchin barren isn’t actually lifeless.

12. People Around The World Eat Sea Urchins

Although eating the spiny, potentially lethal sea urchin may seem unusual, it is really regarded as a delicacy in many cultures. People commonly eat this distinctive and flavorful seafood in Japan, Chile, the Mediterranean, and even on the West Coast of the United States. Along with sea urchins, sea urchin eggs are an expensive delicacy in Japan, costing as much as JPY 40,000 or USD 360 for a kilogram.

Eighty percent of the yearly sea urchin harvest in the globe is consumed by the Japanese, who consume up to 50,000 tons of uni annually. Exporters of sea urchins in South Korea and the US benefit greatly from this.

13. Sea Urchins Fossils Is Northern Europe Folklore

Folklore surrounds a number of different types of fossil sea urchins, with castings in flint made from chalk, of the heart urchin Micraster and the helmet urchin Echinocorys being the most prevalent in the south of England. Both of these, but primarily the latter, are referred to as shepherd’s crowns or fairy loaves by rural residents.

Coastal traditions in Denmark and Southern England, in particular, have different ideas regarding sea urchin fossils. They are used as amulets to ward off bad luck and the evil eye in one religion because it views them as literal thunderbolts. In accordance with another legend, they are used as amulets to ward off various diseases and are thought to be petrified snake eggs.

14. Sea Urchin Mouth Is Called Aristotle’s Lantern

In case you wonder why it is named Aristotle’s Lantern. In fact, the study of its mouth was conducted by Aristotle. The sea urchin’s mouth mechanism is continuous from beginning to end, according to Aristotle. However, it appears to be otherwise because it resembles a horn lantern without its horn panes. The mouth of a sea urchin has been referred to as an Aristotle’s lantern ever since this finding was made.

They will consume just about anything they come upon, including kelp, sea cucumbers, algae, plankton, and dead marine life. They are very helpful in preventing algae development on coral, which can suffocate it and prevent the coral from absorbing sunlight. Every few years, their teeth regenerate and frequently self-sharpen.

15. Not Only Sting, Sea Urchin Has Venomous Bite

Some sea urchins just bite, while others have deadly bites. In contrast to a sea urchin sting, a bite does not leave any spines behind. Pedicellariae, which resemble tiny claw-like pincers and deliver venom, are found at the tips of sea urchin spines. The species has an impact on the symptoms because of the venomous bite.

Additionally, allergic reactions to sea urchins have the potential to be lethal or only mildly severe. Those who have previously had adverse reactions to stings or bites can be especially vulnerable.

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