Slate Pencil Urchin, Heterocentrotus mamillatus
Slate Pencil Urchin (Heterocentrotus mamillatus), also known as Red Slate Pencil Urchin or Red Pencil Urchin, is a species of sea urchin found in the tropical waters of the Indian and Pacific oceans. It is most abundant off the coast of Hawaii.
Specimens found off the coast of Hawaii have bright red spines, more so than others found elsewhere, which generally have yellowish or brown spines. It is similar to Heterocentrotus trigonarius, except that species has longer and darker spines.