This is the Cross-cut Carpet Shell (Ruditapes decussatus), a medium-sized edible bivalve in the family Veneridae. It is commonly found buried in sandy or muddy seabeds in shallow coastal waters.

Location:
Widespread across the eastern Atlantic, from the British Isles south to West Africa, and throughout the Mediterranean Sea. It inhabits intertidal flats, shallow subtidal zones, and sheltered bays with soft sediments.

Average Size:
Adults typically reach 40–60 mm in length, with some individuals growing up to 75 mm depending on environmental conditions.

Family:
Veneridae (Venus Clams)

Species:
Ruditapes decussatus

Shell Description:
The shell is oval and robust, with a slightly inflated profile. Its surface shows concentric growth lines crossed by fine radial ridges, giving a cross-hatched or “decussate” pattern. Colour varies from pale cream to light brown, sometimes with darker zig-zag or mottled markings. The interior of the shell is smooth and white or slightly iridescent.

Habitat:
Lives buried in sand or muddy sand, often partially covered with sediment. It prefers soft sediments in lower shore or shallow subtidal areas where it is protected from strong currents.

Feeding:
The Cross-cut Carpet Shell is a filter feeder. Water is drawn in through one siphon, plankton and organic particles are filtered for food, and water is expelled through the other siphon.

Movement and Behaviour:
Mostly sedentary while buried, it can slowly move using its muscular foot to reposition itself in the sediment, especially after feeding or if disturbed.

Reproduction:
Male and female clams release eggs and sperm into the water. Fertilised eggs develop into planktonic larvae that drift with currents for several weeks before settling into the sediment and growing into adults. Growth and reproduction rates vary with temperature and habitat conditions.

Ecological Role:
By filtering water and stabilising sediment, the Cross-cut Carpet Shell contributes to the health of coastal ecosystems. It is also a food source for birds, fish, and other predators, and empty shells provide shelter for small marine organisms.

Conservation Status:
Common in suitable habitats and widely harvested for food. Populations can be affected by overharvesting, pollution, and habitat disturbance, but the species is not considered globally threatened.