This is the Blue Mussel (Mytilus edulis), also known as the Common Mussel. It is a medium-sized edible bivalve commonly found in intertidal and shallow subtidal zones. The shell is triangular, smooth, and typically blue, purple, or brown, often with concentric growth lines. Adults usually measure between 50 and 100 mm, though some can grow up to 200 mm.

Location:
Widespread across the North Atlantic—along the coasts of Europe (from the White Sea to France), North America (Canadian Maritimes to North Carolina), and into parts of the Southern Hemisphere.

Average Size:
Typically 50–100 mm, with occasional individuals reaching 150–200 mm.

Family:
Mytilidae (True Mussels)

Species:
Mytilus edulis

Ecological Role:
Blue mussels feed by filtering tiny plankton and organic particles from the water, which helps to keep it clean and clear. They often grow close together in large clumps, attaching themselves to rocks and each other using strong fibres called byssal threads. These mussel beds form a kind of living mat that traps sediment and softens the impact of waves and currents, helping to stabilise the seabed and creating a safe home for many other sea creatures.

Movement and Sensory Features:
Although mussels usually stay in one place, they can move short distances by releasing and reattaching with their byssal threads. They sense their surroundings through simple chemical and touch receptors on their soft tissues.

Reproduction:
Male and female mussels release eggs and sperm into the sea. The fertilised eggs hatch into tiny larvae that drift with the currents for a few weeks before settling down and attaching to rocks or other hard surfaces, where they grow into adults.

Conservation Status:
Considered of Least Concern. Widely harvested for food and extensively farmed. Environmental threats include pollution, habitat damage, and ocean acidification, but mussel beds recover well due to rapid recruitment.