The burrowing process of Dentalium (Scaphopoda)



Investigations of the burrowing activity of Dentalium, using cine film and electronic recording techniques, have shown it to penetrate the sand in a series of steps, each termed a “digging cycle”. Cycles involve first, pedal dilation, second, retraction followed by extension and probing of the foot. The epipodial lobes are elevated during pedal dilation and form a secure pedal anchor so that at retraction the shell is drawn down over the foot.

A comparison of the burrowing process in the Scaphopoda with that of the Bivalvia indicates that essentially the same mechanisms and sequence of activities are involved, for in both digging consists of the integration of pedal protraction and retraction with the application of shell and pedal anchors. The principal differences, such as the absence in Dentalium of water jets to loosen the sand and high pressures in the pedal haemocoele, are related to the form of their shell. The strength of the pedal anchor was determined and, relative to the weight of Dentalium, is comparable to that of bivalves. In contrast the probing force was relatively weak since the shell anchor of Dentalium, which holds the shell still during probing, is largely limited to its own weight, whereas that attained by the Bivalvia is principally due to the valves being pressed against the substrate by the opening moment of the ligament.