During a dive off the coast of Tulamben, Bali, Indonesia, photographer Sergio Sarta was scanning a volcanic, dark grey, sandy seabed when he saw a bright-colored organism—a fire urchin with a pair of tiny Coleman shrimps. The fire urchin has quills that are very toxic to humans, and the shrimps avoid this danger by seeking out safe areas between the quills.
also referred to as Shingle Urchins are a a species of sea urchin of the family Echinometridae. they can be found on rocks nears shores of the Indo-West Pacific particularly in Hawaii. they look very different from other sea urchins as their spines have been modified to be flattened and smooth in order to better withstand the waves that crash against the rocks they live on in order to feed on periwinkles and algae. they are usually a maroon color and grow as big as a softball.