Pencil Urchin

Pencil Urchin
Eucidaris tribuloides

The Pencil Urchin is a hardy, thick-spined urchin named for its short, blunt spines that resemble pencils. It’s a nocturnal scavenger that helps clean up algae and detritus — but it’s not fully reef safe, and care should be taken when adding it to coral-heavy tanks.

Quick Stats:

• Care Level: Easy

• Temperament: Peaceful but strong and clumsy

• Color Form: Reddish-brown to tan body with thick, blunt spines

• Diet: Omnivore – grazes on algae and detritus, may nip soft corals if hungry

• Reef Compatible: ⚠️ With caution – may damage or knock over corals

• Water Parameters:

  • Salinity: 1.023–1.025

  • Temperature: 72–78°F

  • pH: 8.1–8.4

  • Alkalinity: 8–12 dKH

• Max Size: Up to 4–5 inches

• Minimum Tank Size: 30 gallons

Why We Like Them:

• Extremely hardy and long-lived

• Unique appearance with thick, stubby spines

• Helps clean up algae and leftover food

• Interesting nocturnal behavior and climbing

⚠️ Pro Tip:
Pencil Urchins are not ideal for coral-heavy reef tanks. In underfed or tight spaces, they may graze on soft corals or sponges. They’re best suited for FOWLR systems, large reef tanks with minimal frags, or as display animals in species tanks.