Slate Pencil Urchin

Heterocentrotus trigonarius

Slate Pencil Urchin, known scientifically as Heterocentrotus trigonarius, inhabits the tropical waters of the Indo-Pacific region. This species can be identified by its large, spiny body, which can grow up to 30 cm in diameter from spine to spine. The spines are potentially harmful to humans if stepped on, so caution is advised when encountering them. It is similar in appearance to Heterocentrotus mamillatus, but the differences can be subtle and require close observation to distinguish between the two species. These urchins are typically found in shallow waters, with a depth range from 0 to 36 meters. They prefer habitats such as fore reefs, outer reef flats, and areas that experience significant wave action. Their distribution includes locations such as the Philippines, New Caledonia, Pitcairn, and the South China Sea, making them relatively widespread in their preferred environment. Slate Pencil Urchins are herbivorous, feeding primarily on algae. They exhibit external fertilization during reproduction, with brooding behavior being common. Eggs are often held on the peristome or around the periproct. After fertilization, embryos develop into planktotrophic larvae before settling to the seafloor and metamorphosing into juvenile urchins. Encounters with these urchins while diving can be intriguing, as they often blend into their surroundings, making them a challenge to spot, yet they contribute to the ecosystem of the reef. The conservation status of Heterocentrotus trigonarius is not evaluated, and there are no specific threats noted for this species. Divers should always be mindful of their environment and the potential impacts of human activity on marine life.