Locomotory and other movements of the trunk of Bonellia viridis (Echiura, Bonelliidae)

Abstract

(With 1 plate and 7 figures in the text)Trunk irrigatory and locomotory movements in the echiuran Bonellia viridis consist of peristaltic waves of constriction. Irrigation is by antero-posterior waves. Locomotion in the burrow may be produced in three different ways: (a) by antikinetic, (b) by synkinetic, and (c) by antikinetic and synkinetic waves in strict alternation. The animal can turn in the burrow and pass out of narrow holes. The animal can move by peristaltic waves also outside its burrow. The versatility of locomotory modes is related to its inhabiting ready-made burrows.

Peristaltic pumping down a porous conduit

“…The lugworm is pictured as residing to one side of its burrow (Riisgård et al 1996), leaving what we take to be an eccentric annular gap that is almost closed over its narrowest section, then moves its surface to cyclically compress the wider side (figure 2a). The worms Urechis caupo, Sabella pavonina and Bonellia viridis exploit motions more like axisymmetric waves (Lawry 1966;Mettam 1969;Schembri & Jaccarini 1977;Pritchard & White 1981), as shown in figure 2(b).…”

“…1996), leaving what we take to be an eccentric annular gap that is almost closed over its narrowest section, then moves its surface to cyclically compress the wider side (figure 2 a ). The worms Urechis caupo , Sabella pavonina and Bonellia viridis exploit motions more like axisymmetric waves (Lawry 1966; Mettam 1969; Schembri & Jaccarini 1977; Pritchard & White 1981), as shown in figure 2( b ).

Figure 2.Sample sinusoidal peristaltic motions in which the pumper maintains a circular cross-section.

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“…In addition, a number of biological pumpers appear to generate peristaltic waves of sufficient amplitude that the conduit almost closes over finite sections of the peristaltic waves (e.g. Lawry 1966;Mettam 1969;Schembri & Jaccarini 1977;Pritchard & White 1981;Riisgård et al 1996;Riisgård & Larsen 2005). A fixed-displacement model (e.g.…”

“…Other examples include the innkeeper worm Urechis caupo (Lawry 1966; Pritchard & White 1981), the peacock worm Sabella pavonina (Mettam 1969) and the spoon worm Bonellia viridis (Schembri & Jaccarini 1977), which differ from the lugworm in their style of peristalsis: these worms pump water axisymmetrically through an annular gap left open around their bodies, whereas the lugworm has been portrayed as pumping along a conduit spanning only a fraction of the burrow's circumference (see figure 1).…”