Crown of thorns starfish are one of the sea creatures that caused damage to coral reefs. They fed on stony corals (Scleractinia). My friend Leo once joined a movement to collect this sea star somewhere in Samal Island because there was a population increase of this species in that area. Their consuming the reefs faster than it can regenerate itself.
Brittle stars are closely related to starfish, they are also known as serpent stars”. Found many of them in the shallow water, rocks, crevasses, holes, and grasses. Their whip-like arms were flexible and are used for locomotion.
Protoreaster nodosus covers a wide area of the shallow seawater. Also known as Horned starfish. You don’t want to step on it. Underwater, their spines really looked frightening to me, especially the large ones.
Sea urchins belong to phylum Echinodermata and makes up the class Echinoidea. Careful not to stepped on these creatures, their spines were painful when penetrated to the skin. It must be removed right away. Their spines were also movable, it protects them from predators. The photo above is its oral surface, where it has the mouth.