Bivalve mollusks: fluid dynamics of burrowing.
When bivalves burrow into soft substrates the foot is first extended and then dilated to obtain a firm anchorage before retraction pulls the shell downward. Pedal dilation is principally caused by adduction of the valves. The hinged shell futnctions as a hydraulic machine in which the strength of the adductor muscles is transferred to the distal part of the foot by means of the body fluids.
Trueman
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