Pencil Urchin

Pencil Urchin – Eucidaris sp.

The Pencil Urchin is a hardy, thick-spined urchin featuring a brown to mottled body with short, club-like spines that radiate in all directions. Adults typically reach 4–5 inches in diameter (including spines) and may develop coralline algae on their spines as they age. Primarily nocturnal, this species hides in rockwork during the day and emerges at night to graze, often feeding on algae films, sponges, sea squirts, and other small invertebrates. Its strong grip and powerful spines mean it should never be forcibly removed from crevices, as this can cause injury.

A well-established aquarium of 55 gallons or larger with ample live rock, stable rockwork, and multiple hiding spots is recommended. Pencil Urchins should be added only to mature systems with low nitrate levels and no history of copper-based treatments, as they are sensitive to poor water conditions. Keep in mind they may dislodge loose aquascaping and can be destructive to corals, so placement in mixed reefs requires caution.

As an omnivore that naturally consumes algae and small invertebrates, provide supplemental feedings of Ocean Nutrition Formula 2, Hikari Spirulina Brine Shrimp, San Francisco Bay Brand Spirulina Mysis, and New Life Spectrum Algae Pellets. For additional nutrition, offer Julian Sprung’s Sea Veggies in an algae clip alongside these foods for balanced health.

Approximate product size: 1.5"–2.5" body size