Purple Urchin

Purple Urchin: The Tuxedo Algae Grazer

The Purple Urchin is the primary common name for a color morph of the charming Tuxedo Urchin, scientifically known as Mespilia globulus. This small, hardy sea urchin is one of the most popular invertebrates for reef aquariums, valued for its voracious appetite for nuisance algae and its striking, easily recognizable appearance.

Its test (body) features a beautiful pattern of short, dense spines with contrasting skin. The "Purple" or "Blue Tuxedo" variant exhibits a body with vivid blue or purple markings between rows of short, light-tipped spines, giving it a distinctive "tuxedo" appearance. This species is famous for its decorating behavior, often carrying pieces of shell, rubble, or small frags on its back for camouflage.

Reaching a maximum test size of about 3 inches (7-8 cm), the Purple Urchin is one of the smaller sea urchins kept in the hobby, making it suitable for smaller, established reef tanks of 20 gallons or more. It is generally easy to care for but requires stable, clean water and a steady supply of algae.

Diet & Compatibility:

• Diet: This urchin is a dedicated Herbivore / Algivore. It is one of the most effective grazers for common nuisance algae, including hair algae and film algae, which it scrapes off the rockwork and glass.
• Feeding: It thrives on a naturally occurring algae mat in a mature tank. If the algae supply is exhausted, it must be supplemented with dried seaweed (Nori) or algae wafers, typically placed on the rock near the urchin, to prevent starvation (indicated by spine loss).
• Reef Compatibility: It is generally Reef Safe With Caution. While it does not consume coral tissue, its movement and decorating habits mean it will easily knock over unsecured coral frags and small pieces of rock. It may also graze on desirable coralline algae.
• Temperament: It is Peaceful and Solitary. It is safe to keep with all peaceful fish and most invertebrates. Its short, blunt spines are non-venomous (unlike the Longspine Urchin), making it one of the safer urchin species for the hobbyist, though care should still be taken during handling.
• Tankmates to Avoid: It is a natural prey item for large predators such as Pufferfish, Triggerfish, and Large Wrasses, which should not be housed with this urchin.

Quick Facts

• Scientific Name: Mespilia globulus
• Primary Common Name: Purple Urchin
• Other Common Names: Tuxedo Urchin, Globe Urchin, Pincushion Urchin, Blue Tuxedo Urchin
• Origin: Indo-Pacific
• Max Size: 3 inches (7-8 cm) Test Diameter
• Temperament: Peaceful / Solitary
• Diet: Herbivore / Algivore (Algae on rock and glass)
• Minimum Tank Size: 20+ Gallons (Established systems only)
• Reef Compatibility: With Caution (May move unsecured objects)