A sea urchin's body is covered in sharp spines.
Having pointy spikes to protect themselves.
A sea urchin is covered with very long, quite sharp spines. I know a scuba diver who banged one with his knee and had to go in for surgery.
Protect it from predators.
They protect the sea urchin from predators, help in movement and burrowing, and they help them with camouflage.
Sea urchins have several adaptations to help them survive. To protect themselves from predators, sea urchins will react immediately if something sharp touches their shell and they will point all of their spines towards the area being poked. They are also light-sensitive. This is why they are nocturnal. This light sensitivity also allows sea urchins to move their spines in reaction to shadows. In order to protect themselves from being swept away from the powerful ocean currents and waves, sea urchins lodge themselves into holes or crevasses. Finally sea urchins, somewhat like starfish, have a certain regenerative ability. If a spine is damaged or lost, a sea urchin can rebuild it. However if there is too much extensive damage to the test, the sea urchin won't be able to heal it.
No. Sea urchins live in the sea.
The structural deference between them is that Sea urchins are more globular whereas sand dollars are flattened. Unlike sea urchins, the sand dollars burrow themselves when threatened. Sand dollars have anus opening at their back side whereas the sea urchins have it at the top.
More sea urchins.
The classification of a Sea Urchin is Echinoidea
there are excatly 3million purple sea urchins
sea urchins eat kelp.
They try to camouflage themselves.