It's obvious why echinoderms were named that way
There are about 7,000 different species of echinoderms in the world in total. They are found in the seas and oceans around the world.
Some extinct echinoderms reached monstrous sizes, up to 65 feet (20 meters) in diameter. But most of them were quite harmless creatures.
Scientists know about 13,000 species of extinct representatives of this type of animal.
All species of echinoderms, without exception, lead an exclusively bottom-dwelling lifestyle. Some of them even don't need sunlight.
They can be really hardy. Starfish, for example, is found at depths of up to 28,000 feet (8,500 meters), where the water pressure reaches enormous values.
Starfish live at greater depths than any other echinoderms
Some echinoderms, such as sea cucumbers, are widely eaten. They are considered a real delicacy in some countries.
Some of them, for example, sea urchins, lead a stationary lifestyle. Others, like starfish, move quite actively.
Many various echinoderms have remarkable regenerative abilities. Starfish of some species can actually grow a new body if they have at least one ray left.
The name of these animals (it came from the Ancient Greek language) is due to their appearance. The skin of most of them is actually covered with thorns or spines.
Echinoderms can also be poisonous. Some of them are poisonous enough to kill a human.
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The first echinoderms evolved on our planet about 520 million years ago, long before the first dinosaurs.
Some of them are considered harmful species. Sea stars of the crown of thorns species, for example, destroy corals, and their active reproduction, in general, threatens them with complete extinction. One adult crown of thorns (by the way, they are very poisonous) can destroy up to 10-20 sq. feet (1.5-2 m²) of corals per day, absorbing the necessary nutrients from them.
Most echinoderms have shrunk in comparison to their ancestors over hundreds of millions of years of evolution but otherwise have not changed at all.
Some of their species are vital for the ecology of the world's oceans. Sea cucumbers constantly sift through the bottom sand and absorb dead organic matter from it.
Echinoderms cannot control the composition of their body's saline fluids, and therefore any change in the salinity of the water is deadly for them.
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