easier penetration. Increased pressure in the foot, and relaxation of 

 transverse muscles distally, causes dilation. Dilation must precede 

 retraction, to provide firm pedal anchorage so that the shell can be pulled 

 down. An important part of the digging cycle is the recovery of the clam 

 near the end of the cycle, in which valves are opened by the elasticity of 

 the ligament. - J.L.M. 



1822 



Trueman, E. R. 1967. 



Activity and heart rate of bivalve molluscs in their natural habitat. Nature 

 214 (5090) : 832-833. 



Reports research on Cardium edule and Donax vittatus . The ability of 

 Mevcenavia (Venus) mevcenavia to respire anaerobically is mentioned. - J.L.M. 



1823 



Trueman, E. R. 1968. 



The burrowing activities of bivalves. In Studies in the Structure, 

 Physiology and Ecology of Molluscs. Vera Fretter (ed.) . Academic Press Inc. 

 (London) Ltd. and Academic Press Inc., New York: 167-186. 



Mevcenavia mevcenavia and other species have been studied. This is largely a 

 review article, summarizing work of the author and others. Papers on 

 M. (Venus) mevcenavia are abstracted elsewhere in this bibliography. Bivalves 

 dig by a series of steps, a "digging cycle", which continue until the animal 

 is beneath the surface. The activity has 6 phases, which integrate pedal 

 protraction and retraction with opening and closing of valves, much of the 

 body musculature playing a part in each cycle. The hinged shell is the basis 

 of a fluid-muscle system which allows the strength of adduction to be used in 

 digging. Adduction generates high pressures in haemocoele and mantle cavity 

 equally and simultaneously. In the haemocoele this pressure gives rise to 

 the characteristic dilated form of the foot to give secure anchorage so that 

 at retraction the shell is drawn down. Pressure in the mantle cavity produces 

 powerful jets of water which loosen the adjacent sand. At each step the foot 

 probes, using intrinsic pedal muscles at relatively low hydrostatic pressure, 

 while the shell is held in place by the elastic ligament pressing valves open 

 against the substrate. Hinge teeth maintain contact between the valves 

 dorsally during digging, when valves are gaping ventrally. It is possible 

 that tissues adjacent to and between the teeth contain tactile receptors. 

 Little is known about nervous control of the digging cycle. Evolution of the 

 bivalved shell seems to have been an adaptation for active burrowing. By the 

 form of their shell, bivalves have been able to utilize the double fluid 

 muscle system for burrowing and have become among the more successful 

 inhabitants of soft substrates. Rate of probing varies widely between' 

 species, e.g., Ensis avcuatus 90 probes/min, M. mevcenavia 16, and Mya avenavia 

 1. Diagrams of a generalized bivalve at various stages of the burrowing cycle 

 probably were drawn from M. mevcenavia, - J.L.M. 



1824 



Trueman, E. R. , A. R. Brand, and P. Davis. 1966. 



The dynamics of burrowing of some common littoral bivalves. J. Exper. Biol. 

 44 (3) : 469-492. 



A detailed description of burrowing activities and mechanisms of 4 common 

 littoral bivalves with very different shell shapes and habits. Mevcenavia 

 mevcenavia was not included, but it appears that the general picture for 

 Ensis holds good for other "normal" bivalves such as the Veneridae: a) 

 protrusion of foot into substrate until fully extended (hakenform) ; b) 

 dilation of distal end of foot to form an anchor (schwellform) ; and c) pull 

 downwards by contraction of pedal retractor muscles (grabstufe) . The paper 

 is illustrated with clear line drawings. - J.L.M. 



507 



