Also known as Long-spined Sea Urchin, Diadema Urchin, Needle-spined Urchin
Black longspine urchins are vital reef grazers that navigate coral crevices by sensing light shifts with sensitive photoreceptor cells across their body surface. During the day, they often gather in defensive aggregations with spines interlocked, emerging after dark to scrape turf algae from limestone substrate. Their spine canopy provides crucial nursery shelter for juvenile cardinalfishes and small commensal shrimps.
Not EvaluatedConservation statusIUCN Red List categoriesLCNTVUENCREWEXNot Evaluated — not placed on the risk ladderRed List categories, explained →
Key facts
Diet & prey
Filamentous turf algae
Macroalgae
Encrusting biofilm
Predators
Titan triggerfish
Pufferfish
Giant triton
ThreatsOcean acidification, coral reef degradation, water pollution, and marine heatwaves
HabitatsShallow coral reefs, rocky shores, lagoons, and seagrass beds
Life span4–8 years
Size / weightNot available
Classification
OrderDiadematoida
FamilyDiadematidae
GenusDiadema
SpeciesDiadema setosum
Range & activity
Range data is not available yet.
Safe observation
Interaction riskVery high
Low
Moderate
High
Very high
Why interaction risk is very high
Spines easily penetrate skin and inject mild venom; maintain careful buoyancy around reef surfaces.
Why it is dangerous
Spines are brittle, hollow, and coated in mild toxin; they shatter inside puncture wounds, causing burning pain, swelling, and risk of secondary infection.
How to recognize a risky encounter
Look for dense clusters of exceptionally long, dark needle-like spines with five distinct white spots visible on the central body dome.
What to do
Never handle or step on live specimens; if punctured, soak the wound in hot water and seek medical assistance to safely remove spine fragments.
Responsible observation
Diving Etiquette: Maintain neutral buoyancy and keep hands and fins well clear of reef crevices.
Footwear: Wear thick-soled reef booties when wading in shallow lagoons to prevent accidental punctures.
