Spiney urchins are very strange animals. Well named, and if you bump into one, you get stuck! Their spines aren't poisonous, but break easily, so you have a bit of a wound for a while, until the bits dissolve. Best to not bump them! This photo also shows a purple sea fan, a type of coral animal (!!) The brownish, and the white are both Blade Fire Coral, that's a real 'don't touch' coral, it burns, but just for an hour or two. The white color is bleached, not good, the sea was too hot. Sometimes coral can recover from bleaching, but sometimes not.
These urchins have been feasting! See how the rock bottom is clean and white in their vicinity. They move around slowly using tiny rubbery feet that are somewhat sticky. They also use their feet to pick up food, algae, and stuff it in their mouth, which is in the middle of their bottoms.
Looking down at lots of urchins in the rubbly rocks. If you get very close, they can sort of see you, and they wiggle their spines at you. "Go away!!" they cry in their tiny voices that we cannot hear. Funny little cows of the sea, happy to just graze around.