. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. MECHANISM OF BURROWING IN ARENICOLA 375 burrowing. The latter has an essentially single coelomic system in contrast to the double system of the bivalves, which consists of the haemocoele, the hydro- dynamic equivalent of the coelom in Arenicola, and the pallial system. Many bivalves thus have the advantage of being able to eject water from their mantle cavity during digging to loosen the sand adjacent to the shell (Fig. 4a, C). In both the thrust used in initial penetration is limited by the weight of the animal since any fo
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. MECHANISM OF BURROWING IN ARENICOLA 375 burrowing. The latter has an essentially single coelomic system in contrast to the double system of the bivalves, which consists of the haemocoele, the hydro- dynamic equivalent of the coelom in Arenicola, and the pallial system. Many bivalves thus have the advantage of being able to eject water from their mantle cavity during digging to loosen the sand adjacent to the shell (Fig. 4a, C). In both the thrust used in initial penetration is limited by the weight of the animal since any force in excess of the weight causes the animal to be pushed back from the sand. Further penetration of a bivalve consists of a series of step-like movements, each termed a "digging cycle," which were well recorded by Quayle (1949) in a study of the digging movements of Venerupis. Each digging cycle involves the integration of adduction and the reopening of the valves with retraction and pro- traction of the foot. Adduction causes high pressure in the haemocoele and as a consequence the foot becomes swollen to form a pedal anchor (Fig. 4a) (Trueman, 1966b). Immediately after adduction the retractor muscles, equivalent to the longitudinal muscles of Arenicola, contract, pulling the shell down and sustaining E u ~ 1 V 3 in P in y 9 a°. r~ ~r~ i^ ' 5s FIGURE 5. Recording of the pressures produced in sand by the burrowing of Mactra subtruncata. At the commencement the bivalve is lying on the sand and the foot penetrates by probing (P). A succession of adductions of the valves and pedal retractions (AR) follow, giving first (left) negative swings, when the foot alone is beneath the sand, to be replaced by large positive pressures (right) when the valves have entered the sand. These are caused by ejection of water from the mantle cavity at adduction. the pedal pressure and anchorage. Subsequently the opening moment of the hinge ligament opens the valves and presses them agai
Size: 3032px × 824px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
