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Pencil Urchin

(Eucidaris tribuloides)

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 Quick Care Facts

• Care Level: Moderate   • Temperament: Peaceful   • Maximum Size: 6"
• Diet: Omnivore   • Aquarium Level: Substrate & Rocks   • Minimum Tank Size: 30 gallons
 • Reef Compatible: Yes   • Water Conditions: 72-78° F, dKH 8-12, pH 8.1-8.4, sg 1.023-1.025
• Supplements: None   • Coloration: Brown, Tan
• Origin: Caribbean • Family: Cidaridae   • Species: Urchins

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Native Habitat and Species Information

Pencil Urchin native habitat, distribution, behavior & aquarium compatibility.

The Pencil Urchin of the Eucidaris genera has a brown and tan, sometimes mottled body with stubby, thick spines radiating out in all directions. Pencil Urchins are primarily omnivorous scavengers that will generally hide in rock caves or crevices during the day, then move about the live rock or reef during the night looking for algae or meaty foods to eat. This species should be handled carefully and do not try to pry it out of a hole or off of the reef, as you will break its spines before it will let go of its hold.

Over time it is common for the spines of the Pencil Urchin to become covered with coralline and other types of algae as this species is stationary for most of the daylight (aquarium light) hours, which allows for algae growth to on its body to occur. This is a peaceful species that makes an excellent aquarium cleaner and provides a different look then the more common snail and crab aquarium cleaners.

Aquarium Care

How to successfully keep Pencil Urchin in the home aquarium.

The Pencil Urchin will spend most of the day in the shelter of the live rock or reef; however, at night it will come out and forage for food, looking particularly for algae covered areas and smaller invertebrates like sea squirts or sponges. It can be destructive to some corals and the rock formations should be sturdy, since the Urchin can dislodge rocks as it moves around the tank, thus this species will not be suitable for all reef aquariums.

It requires an aquarium with multiple hiding places and live rock on which it can graze and seek shelter. The Pencil Urchin is very sensitive to high levels of copper-based medications and will not tolerate high levels of nitrates. If water conditions are poor, it will shed its spines. It is extremely difficult to breed in an aquarium and has no distinguishing characteristics to help differentiate it from its mate.

Feeding & Nutrition

How to feed and provide proper nutrition for Pencil Urchin.

Pencil Urchins eat both marine algae and meaty foods that it comes across while scavenging the live rock and substrate of the aquarium. It is important to have a good amount of live rock for the Pencil Urchin to scavenge for food, as live rock provides a place for marine algae, sponge and other smaller invertebrates like sea squirts to live and grow. Pencil Urchins will also accept dried seaweed or meaty foods as a supplement food source.

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