Diadema setosum – Black Long Spine Urchin
🔹 Quick Facts
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Scientific Name: Diadema setosum
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Common Name: Black Long Spine Urchin
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Family: Diadematidae
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Origin: Indo-Pacific, including Red Sea, Indian Ocean, and Western Pacific reefs
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Reef Safe: ✔ Yes (with caution – may knock over corals)
🔹 Identification
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Jet black, rounded body with needle-like spines that can reach up to 30 cm (12 inches) in length.
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Often displays five distinctive white dots around the central body.
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Has a bright blue or orange ring around the anus – a unique identifying feature compared to other urchin species.
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At night, tube feet and pedicellariae (tiny claw-like structures) can be seen moving actively.
🔹 Behavior
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Nocturnal grazer – hides in crevices during the day and comes out at night to feed.
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Moves slowly but is very effective at clearing algae.
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Uses its long spines as defense against predators – fish generally avoid them.
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Can accidentally dislodge rocks and corals when climbing.
🔹 Diet
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Primary diet: microalgae and filamentous algae.
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Will graze on coralline algae (sometimes frustrating for reef keepers).
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If natural algae is lacking, it should be fed dried nori, spirulina, or herbivore pellets.
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A well-fed urchin = better algae control + longer survival in the reef tank.
🔹 Tank Requirements
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Tank Size: 75 gallons minimum (needs plenty of rock and grazing space).
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Lighting: Not picky – thrives in reef lighting.
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Water Parameters:
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Temperature: 72–78°F
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Salinity: 1.023–1.025
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pH: 8.1–8.4
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Nitrates: <10 ppm
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Phosphates: <0.1 ppm
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Needs a mature aquarium with stable water and plenty of natural algae.
🔹 Reef Compatibility
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✔ Safe with corals (does not eat them)
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✔ Safe with fish (most avoid the spines)
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❌ Not safe with predators like triggers, puffers, or large wrasses (they may try to bite it)
🔹 Benefits
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Excellent algae control for reef aquariums.
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Adds unique, exotic movement and appearance to the tank.
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Natural part of the reef ecosystem – creates balance.