Long-spined sea urchin

Geographical Origin and Habitat: Diadema setosum is widely distributed throughout the tropical waters of the Indo-Pacific, from the Red Sea and East Africa to Australia, Japan, and Hawaii. It inhabits shallow coral reefs, sandy lagoons, and seagrass beds, often aggregating in large groups.

Taxonomy: It belongs to the class Echinoidea, order Diadematoida, family Diadematidae. It is one of the most evolutionarily stable and ancient sea urchin species, recognized worldwide by its unique morphology and distinct color patterns.

Social Behavior: Primarily a nocturnal invertebrate. During the day, it shelters beneath rocky overhangs or corals, emerging at night to graze on the substrate. It displays defensive behaviors by actively tilting its long spines toward nearby shadows or movement.

Coloration and Sexual Dimorphism: Features a deep black body and extremely long black spines, marked by five blue-white spots arranged in a star pattern on its test. A bright orange anal ring at the center of the body is its diagnostic feature. There is no visible external sexual dimorphism.

Tank Setup: Requires a large aquarium, preferably over 250-300 liters, to accommodate its extremely long spines without damaging corals or restricting its movement. Rockwork must be securely stacked, as the urchin's raw strength can easily dislodge or topple loose structures.

Diet and Feeding: An excellent herbivore that consumes massive amounts of film, hair, and coralline algae. If natural algae levels are low, its diet must be supplemented regularly with dried nori sheets, seaweed, or sinking spirulina pellets to prevent starvation.

Water Quality: Demands stable parameters: temperature of 24-27°C, pH of 8.1-8.4, specific gravity of 1.022 to 1.025. It requires proper calcium and magnesium levels to grow and maintain its calcareous test and spines. Absolutely zero tolerance for copper treatments.

Compatibility and Tankmates: Safe with most corals and fish, though it may scrape off decorative coralline algae from live rocks. Avoid housing them with natural predators of sea urchins, such as large triggerfish, pufferfish, wrasses, or large hawkfish.

Aquarium Breeding: Breeding in captivity is exceptionally rare and complex. They spawn by releasing gametes into the water column. The resulting planktonic larvae are very delicate and are almost always removed by mechanical filtration systems.

Risks and Diseases: The long spines are sharp, brittle, and mildly venomous; a sting causes sharp pain and irritation in humans, requiring careful handling. Spine loss is a primary indicator of severe stress, poor water quality, or starvation.