This is a Dog Cockle (Glycymeris glycymeris), a species of marine bivalve mollusc in the family Glycymerididae. Found along the coasts of western Europe, including the British Isles, the North Sea, and the Mediterranean Sea, this species is characterised by its large, thick, almost circular shell, often brown or reddish with concentric growth lines. The sturdy shell allows it to burrow into sandy or muddy seabeds, providing protection from predators.

Location:
Northeastern Atlantic and Mediterranean—from Norway to the Mediterranean—burrowing in sandy or muddy seabeds at depths of approximately 5 to over 100 metres.

Average Size:
Typically up to 6.5 cm in diameter, though larger examples exist.

Family:
Glycymerididae (Dog Cockles)

Species:
Glycymeris glycymeris (formerly Pectunculus glycimeris)

Ecological Role:
A filter feeder, the Dog Cockle contributes to water clarity by filtering plankton and organic particles. Its burrowing behaviour helps stabilise sediment and supports marine biodiversity by providing microhabitats for other small marine organisms.

Reproduction:
Separate sexes; fertilisation is external. The larvae drift in the open water as plankton before settling on the seabed as juveniles.

Conservation Status:
Not currently considered threatened, but local populations may be affected by pollution and habitat degradation. Clean, healthy waters are important for sustaining Dog Cockle populations and the wider marine environment.

Collection Date:
Collected on 19 July 1900.