Are the spines of the Long-Spined Urchin venomous?

Yes, their spines possess a mild venom. A puncture will usually feel similar to a bee sting, though the primary danger is the brittle spine snapping off under your skin, which can lead to infection.

Will a Long-Spined Urchin eat my corals?

They are generally considered reef safe and do not eat coral polyps. However, they are enthusiastic grazers of coralline algae and can accidentally bulldoze or knock over loosely attached coral frags.

Why is my urchin dropping its spines?

Spine loss is a major red flag indicating stress. It is usually caused by poor water quality, high nitrates, sudden changes in salinity, or starvation. Immediate water testing is required.

Do I need to feed my Long-Spined Urchin?

If your tank has plentiful nuisance algae and coralline algae, it may sustain itself. However, if the tank is very clean, you must supplement its diet with dried seaweed (nori) or algae wafers to prevent it from starving.

Can I keep multiple Long-Spined Urchins together?

Yes, they are completely peaceful towards their own kind. However, given their large size and voracious appetites, your aquarium must be exceptionally large to provide enough algae for multiple individuals.

MarineMarineIntermediate

Long-Spined Urchin

Diadema setosum

The Long-Spined Urchin is a striking marine invertebrate renowned for its exceptionally long, black spines and voracious algae-eating habits.

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Ideal Conditions

Temperature: 24 – 28 °C
pH range: 8.1 – 8.4
Hardness: 15 – 25 dGH
Salinity: 1.023 – 1.026 SG
Adult size: 15 – 30 cm
200L minimum: 200 litres+
Lifespan: 5 – 10 years
Diet: Herbivore
Water flow: moderate
Preferred setup: Mature reef or FOWLR with ample live rock and open swimming areas

About the Long-Spined Urchin

Native to the Indo-Pacific, Diadema setosum is easily identified by its long, hollow, black spines, which can reach an impressive length. It features a distinctive orange ring around its anal cone and striking iridescent blue lines or spots along its body. Primarily nocturnal, it tends to wedge itself into reef crevices during the day and emerges at night to graze on surrounding algae.

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Is it right for your tank?

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Where Long-Spined Urchin comes from

Native range

Indo-Pacific, Red Sea

Countries / regions

Australia, Indonesia, Japan, Egypt

Habitat

Coral reefs, lagoons, and rocky substrates in shallow coastal waters.

Widespread across the Indo-Pacific and recently recorded as an invasive species in the eastern Mediterranean Sea.

Similar species

Tuxedo Urchin
Mespilia globulus
Pincushion Urchin
Lytechinus variegatus
Banded Sea Urchin
Echinothrix calamaris

We’re adding more full species guides as the catalogue grows.

Compatible tank mates

Reviewed guidance based on this species' recorded traits.

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Ocellaris Clownfish
Amphiprion ocellaris
Peaceful fish that occupy higher levels of the tank and will entirely ignore the urchin.
Great
Yellow Tang
Zebrasoma flavescens
Peaceful fellow herbivores that cohabit easily, provided the tank has enough algae for both.
Great
Skunk Cleaner Shrimp
Lysmata amboinensis
Harmless invertebrate companions that will not bother the urchin's spines.
Great
Clown Triggerfish
Balistoides conspicillum
Large triggerfish are natural predators of sea urchins and will actively break their spines and consume them.
Not recommended
Dogface Puffer
Arothron nigropunctatus
Puffers have strong, beak-like mouths designed to crush invertebrate shells and tests.
Not recommended

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