Heterocentrotus trigonarius
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Heterocentrotus trigonarius, commonly known as the slate pencil urchin or red slate pencil urchin, is found in the tropical waters of the Indo-Pacific region. Heterocentrotus mamillatus is a similar, related species.
Heterocentrotus trigonarius can grow to 30 cm (12 in) in diameter (spine-to-spine). The spines are potentially harmful to humans if trodden on.