Dynamics of burrowing and pedal extension in Donax serra (Mollusca: Bivalvia)



Donax serra burrows powerfully and rapidly in the same manner as other infaunal bivalves except that the turgidity of the foot is increased by a standing pressure of up to 3 kPa in the pedal haemocoel. The standing pressure, upon which probing and adduction pulses are superimposed, is derived from muscular tension acting on the blood in the pedal haemocoel, which is held at near constant volume by the closure of Keber's valve. Blood flow through the foot is thus reduced to a minimum at the time of maximal pedal activity and it is possible that pedal respiration is anaerobic during burrowing.

Extension of the foot is brought about by blood flow and antagonistic musclc action using blood in the pedal haemocoel as the fluid of a classical fluid-muscle system. There is no evidence of the presence of a muscular antagonistic system causing pedal protraction as occurs in the columellar muscle of some cyrtosome molluscs.