Banded Wedge Shell (also known as the Butterfly Shell)
Phylum: Mollusca; Class: Bivalvia; Order: Cardiida; Family: Donacidae; Genus: Donax; Species: Donax vittatus · Donacidae (Wedge Shell or Bean Clam family) · Bivalve (two-shelled). This specimen is a 'butterfly' pair, meaning both valves are still attached at the hinge. Shape is cuneiform (wedge-shaped).
Species
Donax vittatus
Shell Type
Bivalve (two-shelled). This specimen is a 'butterfly' pair, meaning both valves are still attached at the hinge. Shape is cuneiform (wedge-shaped).
Family
Donacidae (Wedge Shell or Bean Clam family)
Size
Approximately 25-35mm in length. This is a fully mature adult specimen; the species typically ranges from 15mm to 38mm.
Color & Pattern
Glossy exterior with a creamy-yellow to light tan base. Features faint white concentric growth lines and subtle radial striations. The interior possesses a polished, porcelaneous white finish, often with a hint of violet or purple near the margins in fresh specimens.
Rarity
Very Common. These are staple finds on sandy Scottish beaches like Troon, often appearing in the thousands after storms.
Habitat
Found in the intertidal and shallow subtidal zones, specifically in clean, well-oxygenated sandy beaches with high wave energy. They live buried just beneath the surface of the sand.
Geographic Range
North Atlantic and European coasts, ranging from Norway and the British Isles (highly common in Scotland) down to the Mediterranean and Northwest Africa.
Description
An elegant, wedge-shaped bivalve with a highly polished, glossy periostracum. The shell is thickened and sturdy for its size, an adaptation for life in turbulent surf zones. The anterior end is long and rounded, while the posterior end is short and abruptly angled, giving it the characteristic 'wedge' look. When opened flat, the two valves resemble the wings of a butterfly.
Key Features
Distinguished by its wedge shape, glossy texture, and finely serrated (crenulated) inner ventral margins. The hinge features two cardinal teeth in each valve. Its asymmetrical profile—where the beak (umbo) is positioned toward the rear—is a diagnostic trait.
Collector Value
Minimal monetary value ($1-$3) due to abundance, but 'butterfly' pairs with intact hinges are preferred over single valves for educational displays and aesthetic coastal decor.
Condition Notes
Good condition. The hinge ligament is intact, which is desirable for collectors. Minor sand abrasion is visible on the margins, and slight sun-bleaching has faded the deeper purple tints often seen in live specimens. Collectibility Grade: Fine.
Interesting Facts
These mollusks are 'surf-riders'; they use their muscular foot to pop out of the sand as the tide comes in, allowing the waves to carry them up the beach to feed, and then re-bury themselves rapidly. Historically, they were harvested for food in coastal villages.
Ecological Role
Primary consumer and filter feeder, playing a vital role in cleaning coastal waters. They are a significant food source for shorebirds (like Oystercatchers) and flatfish (like Plaice).
Similar Species
Donax variegatus (usually more colorful and smaller) and Donax semistriatus. It can be distinguished from the common cockle or tellin by its distinctively flat, angled posterior edge.
Beach Finding Tips
Best found at Troon during low tide, specifically near the strandline after a period of heavy surf. Look for 'butterfly' pairs in the fine-grained sand patches where the receding water leaves a smooth surface.
Notes
Troon Scotland