Lingulides position their shells at the top of their burrows. The shell is held there by hydrostatic pressure exerted by the body cavity and the valves on the walls of the burrow; the pedicle plays no role in keeping the animal in this position. Lingulides cannot live in coarse or muddy substrata because the walls of the burrow do not support the shell in its normal filtering position. Rapid withdrawal into the burrow is an escape reflex or protective reaction that may be observed if the setae (bristles) on the front margin of the animal are touched or if there is a sudden change in light intensity.
The ventral valve of the discinids is always oriented towards the surface on which it lives. This positioning is related to the orientation of the larva when it settles on the substrate. Discinids are attached by a highly muscular pedicle to hard substrates.
The craniids are generally gregarious (living in groups), preferring to live on hard flat surfaces. They are cemented directly to the substrate by their ventral valves.
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