Clams are bivalve mollusks found in freshwater and marine environments. Though often buried, they possess specialized anatomical features for movement. Their primary method of self-relocation is burrowing, used for protection or feeding.
The Clam’s Muscular Foot
The clam’s muscular foot is its primary tool for movement. This appendage, often tongue-shaped or blade-like, extends from the shell. Highly muscular, the foot operates on a hydraulic principle. When extended into the sediment, blood is pumped into it, causing it to swell and anchor firmly. This hydraulic expansion provides a firm grip, allowing the clam to exert force.
How Clams Burrow
The burrowing process in clams is a coordinated sequence of actions involving the muscular foot and shell movements. Initially, the clam extends its pointed foot deep into the sand or mud. Once positioned, the foot’s tip inflates with blood, creating a bulbous anchor that firmly grips the surrounding sediment. With the foot securely anchored, the clam contracts its powerful foot retractor muscles, which pull the shell downwards towards the embedded foot.
During this pulling phase, the clam often rapidly closes its two shell valves. It expels water from the mantle cavity, which can temporarily liquefy or fluidize the sediment immediately surrounding the shell, reducing friction and drag. This localized fluidization allows the shell to slide more easily through the substrate. Many clams utilize a “double-anchored wiggle,” alternating between anchoring with the foot and using the shell valves to push and contract, effectively wedging themselves deeper. The entire cycle of foot extension, anchoring, shell adduction, and retraction is repeated, allowing the clam to progressively descend and bury itself.
Beyond Burrowing: Less Common Movements
While burrowing is the predominant form of locomotion for most clams, some species exhibit other, less common movements. Many clams, once settled, remain relatively stationary for long periods. However, certain species, like the razor clam, are known for their rapid and impressive burrowing capabilities, often described as “leaping” or quickly disappearing into the sand. This swift movement is also achieved through the foot and shell actions, leveraging the fluidization of sand to a high degree.
Another notable example of bivalve movement, though not characteristic of most clams, is the jet propulsion used by scallops. Scallops, which are also bivalves, can swim in short bursts by rapidly clapping their shells together. This action expels water from their mantle cavity, generating thrust that propels them through the water, typically as an escape response from predators. Furthermore, some species, such as the hard clam, have been observed to move horizontally across the sediment surface, a behavior sometimes referred to as “walking,” though this is less frequent than their vertical burrowing.