European thorny oyster

Mollusc

Identification & Biology

• IdentificationA striking bivalve with an irregularly shaped shell covered in long, sharp spines. The exterior is often heavily encrusted with sponges, algae, and other organisms. The shell interior is white to pale purple. Cements itself permanently to hard surfaces.
• SizeShell diameter up to 12 cm (excluding spines). Spines can add several centimetres.
• Social HabitSessile (permanently attached to rock). Lives alone or in loose groups on vertical walls and overhangs. Filter feeds by opening its shell slightly to draw in water.
• HabitatRocky walls, cave ceilings, and overhangs. Prefers shaded, vertical or overhanging surfaces with good water flow.
• Depth5 to 50 m. Most common between 10 and 35 m.
• Feeds OnPlankton and suspended organic particles filtered from the water.
• DistributionMediterranean Sea and adjacent eastern Atlantic. Present in Maltese waters on suitable rocky substrates.
• DescriptionSpondylus gaederopus has been prized since antiquity, with shells found in archaeological sites across the Mediterranean dating back thousands of years. In the water, the heavily encrusted shell is difficult to spot, blending completely with the surrounding rock. Only the line of bright orange or red tissue visible between the slightly parted shells betrays its position. The spines deter predators and provide attachment points for encrusting organisms.