Pencil Urchin - Eucidaris tribuloides
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The Pencil Urchin (Eucidaris tribuloides) is a unique and hardy marine invertebrate, recognized for its thick, blunt spines and algae-grazing habits. This peaceful urchin is an interesting and functional addition to reef aquariums, helping control algae while adding visual texture to the tank.
Common Name: Pencil Urchin
Scientific Name: Eucidaris tribuloides
Family: Cidaridae
Size: Up to 6 inches (15 cm)
Temperament: Peaceful
Difficulty: Moderate
Reef Safe: With Caution
Native Region: Found throughout the Caribbean and Western Atlantic, typically inhabiting coral reefs, rocky substrates, and seagrass beds.
Tank Size: Minimum of 30 gallons
Temperature: 74–80°F (23–27°C)
pH: 8.0–8.4
Salinity: 1.023–1.025
Substrate: Live rock and sand with stable surfaces for grazing and shelter.
• Algae Control: Grazes on algae, detritus, and biofilm, helping maintain clean surfaces.
• Behavior: Slow-moving; spines can injure other invertebrates or humans if handled carelessly.
• Diet: Herbivorous—supplement with dried seaweed if natural algae is limited.
• Tankmates: Compatible with most reef fish and invertebrates; avoid predatory species that may damage the urchin.