Groove Burrowing Urchin

Echinoderm

Identification & Biology

• IdentificationA large, heart-shaped sea urchin (irregular urchin) with a domed upper surface and a flattened base. Covered in short, dense, fine spines that give it a velvety appearance. Pale yellow to tan in colour. Unlike regular urchins, it lacks the typical spherical shape.
• SizeTest length up to 9 cm. One of the larger burrowing urchins in the Mediterranean.
• Social HabitSolitary. Lives buried in soft sediment, maintaining a burrow through which it draws oxygenated water. Rarely seen on the surface.
• HabitatSandy and muddy bottoms where it can burrow. Requires deep, soft sediment.
• Depth5 to 200 m. Most common between 10 and 50 m.
• Feeds OnOrganic particles and detritus in the sediment. A deposit feeder that processes buried organic material.
• DistributionEastern Atlantic and throughout the Mediterranean Sea. Present in Maltese waters on suitable sandy substrates.
• DescriptionBrissus unicolor is a burrowing urchin that spends its life beneath the sand surface, rarely seen by divers unless exposed by currents or dredging. Its heart-shaped test is distinctive and is sometimes found washed up on beaches. The fine, velvety spines help it move through sediment and maintain its burrow walls. It plays an important role in bioturbation, mixing and aerating seabed sediments.