Heterocentrotus trigonarius,[1] commonly known as the slate pencil urchin or red slate pencil urchin,[2] is found in the tropical waters of the Indo-Pacific region.

[1] Heterocentrotus mamillatus is a similar, related species.

[2] Heterocentrotus trigonarius can grow to 30 cm (12 in) in diameter (spine-to-spine).

The spines are potentially harmful to humans if trodden on.

This article about a sea urchin is a stub.