Great Scallop

Presentation

The great scallop is a marine bivalve mollusc distinguished by its fan-shaped striated shell made up of two asymmetrical valves. The upper valve is flat and slightly convex, while the lower valve is concave. This animal lives attached to sandy or gravelly seabeds, mainly in the temperate waters of the north-east Atlantic and the Mediterranean. It is highly prized in gastronomy for its flesh and roe, making it a species of major economic importance. Its slow growth and longevity make it a valued indicator for studying marine environmental conditions. It moves occasionally through sharp valve contractions that produce a propulsive water jet.

The shell displays well-marked radiating ribs and varies in colour from reddish-brown to whitish depending on the valve. The animal has numerous simple eyes arranged along its mantle, capable of detecting changes in light and movement. The central adductor muscle is highly developed, allowing rapid closure of the valves.

Characteristics

Indicative values: they vary by subspecies, sex and region.

Habitat and distribution

The species lives on sandy, gravelly, or muddy seabeds at depths reaching up to about a hundred meters. It prefers areas where currents bring a constant supply of suspended food. It is found partially buried, with only the shell edge exposed above the sediment.

Behaviour

This animal usually remains motionless, partially buried in sediment, with the flat valve facing upward. When threatened—such as by an approaching predatory starfish—it can make short jumps by snapping its valves to escape. It is able to detect shadows and movements through its peripheral eyes, triggering an escape or closure response.

Reproduction

The scallop is hermaphroditic, producing both male and female gametes within a single two-colored gonad. Fertilization is external and occurs in open water following gamete release, typically in spring or summer depending on the population. Planktonic larvae drift for several weeks before settling on the seabed and developing their permanent shell.

Peculiarities

It has up to a hundred small blue eyes arranged along the mantle edge, a feature that is rare in bivalves. Its age can be determined by counting the growth lines visible on its shell, similar to the growth rings of a tree.

Threats and conservation

Overfishing driven by strong gastronomic demand represents the main pressure on wild populations. Minimum capture size regulations and controlled fishing seasons have been implemented in several countries to protect stocks. Seabed degradation from certain dredging practices also affects spawning habitats.

References

Profile updated 30 August 2026 · Reviewed by the TunisieVet editorial team.