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.
Location: Sta. Maria/ Class: Echinoidea/ Species: ?