Species encyclopedia

Hatpin Urchin

Diadema setosum


The hatpin urchin prefers sandy beds at the base of coral colonies, between 0 and 25 m below the surface.

This gregarious creature that feeds on algae is often found in groups, particularly during the day.

The urchin can be recognized by its long spines (up to 15 cm) and the orange-red ring around its anus on its posterior. Hatpin urchins are usually black, but their spines can also be lighter in colour (grey, white or purple) or even striped in juveniles.

Defense system

Like all sea urchins, these spines are mobile, allowing the animal to point them toward any danger that may be threatening it.

It is sometimes used as a refuge by shrimp and small fish. The hatpin urchin’s long, thin spines are covered with tiny barbs. These are not venomous but can easily slip into the skin, breaking off and becoming embedded only to later cause infection.

The hatpin urchin can now be found in the Eastern Mediterranean. This extension of its range is undoubtedly due to the movement of its larvae through the Suez Canal.

Indo-Pacific area


Species encyclopedia

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