Heterocentrotus mamillatus, commonly known as the slate pencil urchin, red slate pencil urchin, or red pencil urchin, is found throughout the tropical waters of the Indo-Pacific region, but is most abundant in Hawai‘i. Specimens from Hawai‘i tend to have bright red spines, while specimens from other parts of the Pacific may have yellowish or brown spines.

Heterocentrotus trigonarius is a similar species that has longer and darker spines.

References

• Hoover, John P. (1998). Hawaiʻi's Sea Creatures: A Guide to Hawaiʻi's Marine Invertebrates. Mutual Publishing. ISBN 1-56647-220-2.
• UC Berkeley Moorea Biocode species listing
• "Heterocentrotus mamillatus". Integrated Taxonomic Information System. http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=656058.

Red pencil urchin at French Frigate Shoals.

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