Editing Tusk shell (section)

=== Mantle ===
The [[mantle (mollusc)|mantle]] of a scaphopod is entirely within the shell. The foot extends from the larger end of the shell, and is used to burrow through the substrate. The scaphopod positions itself head down in the substrate, with the apical end of the shell (at the rear of the animal's body) projecting upward. This end seldom appears above the level of the substrate, however, as doing so exposes the animal to numerous predators.  Most adult scaphopods live their lives entirely buried within the substrate.

Water enters the mantle cavity through the apical aperture, and is wafted along the body surface by [[cilia]]. There are no [[gill]]s; the entire surface of the mantle cavity absorbs [[oxygen]] from the water. Unlike most other molluscs, there is no continuous flow of water with a separate exhalant stream. Instead, deoxygenated water is expelled rapidly back through the apical aperture through muscular action once every ten to twelve minutes.