8 unbelievable facts about sea urchins

8.unbelievable facts about urchins that you probably didn’t know.
1. The red sea urchin is the largest of the species.
Big Red sea urchin
In general sea urchins grow to be around 1.18 inches (3 cm) to 3.93 inches (10 cm).
The red sea urchin is the biggest of the species and it will enter adulthood when it reaches 1.96 inches (5 cm) in diameter.
It will then continue to grow until it reaches around 3.93 inches (10 cm), whereas most other sea urchins will stop growing around 1.96 inches (5 cm).
The red sea urchin can be found in the North Pacific Ocean, from as far north as Alaska, to as south as Baja, California.
2. They have zero bones in their body.
Sea urchin 'test' shell
Unlike humans they don’t rely on a bone structure to support their bodies.
Urchins have a shell-like structure which is called a “test”.
The hard shell made from calcium carbonate is similar to that of starfish and sand dollars and is their main form of protection.
The structure consists of small plate segments that enclose the urchin; it looks a bit like the segments of an orange.
As well as the “test” they have spines which help them protect themselves from predators.
3. The flower urchin is the most dangerous in the world.
The Flower Urchin, the most toxic urchin of the seas
Toxopneustes pileolus, known to most as the flower urchin is the deadliest of all.
As described in Guinness Book of Records, the flower urchin contains deadly venom, which can kill a human.
Its venom contains two poisonous elements; Contractin A, which can cause red blood cells to clot and can cause muscle spasms.
The other element is Peditoxin which can cause anaphylactic shock, convulsions and death.
When a human or animal steps on, touches or brushes past the flower urchin, its “flower-shaped” spines will break or pierce the skin of the predator.
4. It is possible for some fish to build up immunities to the flower urchin’s venom.
An orange and white striped clown fish
The clownfish is one of the only species that purposefully try to build immunity to the flower urchin’s venom.
Clownfish will dance around the flower urchin, lightly brushing itself against the spines.
This means they are exposed to a small amount of venom, but not enough to kill them.
After repeating this a few times they become immune to the venom.
You might be wondering why they choose to do this and the reason is so they can eat the parasites that live on the flower urchin.
This relationship is beneficial to both creatures as the clownfish gets food and the flower urchin has its parasites removed.
5. Urchins make for a tasty snack, not just for animals but humans too.
Urchin that have been prepared for people to eat
Not only are there species that eat the parasites off of the urchins, but there are also animals that eat them whole!
Sea urchins have quite a few predators which is surprising given their spines and sometimes venom.
The sea otter is one of their biggest predators; they will eat as many as they can get their hands on.
Some of the most common predators are crabs, large fish, eels and even birds.
Urchins also have the threat of humans, urchin and in particular their row (eggs) are seen as a delicacy in many places.
This threat has caused a large decrease in the population and has caused some species of sea urchins to become endangered because of overfishing.
6. Sea urchins have just 5 teeth!
A closeup of a sea urchin's five teeth
Sea urchins are omnivores and have just 5 teeth, which are held together in the center of its body.
Each tooth has its own jaw to keep it in place; this means it is able to move more freely.
The teeth are made from calcium carbonate and they also have a tongue-like structure alongside them which gives them a beak-like mouth.
Urchins mostly feed on algae found on rocks or corals, as well as any debris or decomposing matter from fish or sea creatures.
7. Urchins have hundreds of tiny feet.
Many black sea urchins on the sea bed
Sea urchins have 5 paired rows of tubular tiny feet called pedicellariae.
These tiny rows are located between the spines.
Each foot is a small sucker like shape which allows the urchin to grip surfaces in order to pull itself along.
The suckers are also useful to help catch food and attach themselves to the ocean floor.
8. Sea urchins can live for up to 200 years in the wild.
Red Sea Urchins
The oldest living species found was the red sea urchin which was dated to be around 200 years old.
In captivity their life expectancy is reduced to around only 30 years, while in the wild is usually over 30 years.
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