Continuous filtering indicates that the
normal position of the lingulide shell is at
the top of the burrow (EMIG, 1982). To
maintain this position (Fig. 408), a weak
contraction of the lateral body muscle layer
produces a hydrostatic pressure on the
body's coelomic cavity; the body volume is
shifted posteriorly and laterally; the valves
gape about 6° to rest against the lateral burrow
walls, which act as supports; and the lophophore
extends to become functional
within an enlarged pallial cavity. The normal
life position is static and can be maintained
without much effort. The pedicle plays no
role in the maintenance of this position.
Occasional scissorlike movements of the
valves assist in maintenance of the burrow
(Fig. 409).