Tusk shell molluscs feed on small organisms in the muddy sea bottom. They collect their food by means by the ceptacula, then scrape off the food using a well developed radula that has wide flattened teeth. The mouth is near the larger front end, at left in the diagrammatic picture above. Their rear end, at right in the picture, is where the ciliary currents enter and leave, and its narrow opening usually has a smooth edge. In the picture, one can also see the well developed digestive system, which shows as an "x-ray" view (in green) through the mantle (in pink). The fan shaped organ is a liver, not a gill, while the black dots represent nerve ganglia. 

 The mollusc has no gills. Exchange of oxygen and carbon dioxide takes place directly through the thin tubular mantle and the water. The mantle curves around the viscera, to almost enclose the mollusc in a cylinder. Interestingly, the tubular mantle acts like a peristaltic pump, ejecting wastes with the exhaled water at the rear end, in pulses every 10-12 minutes. The mollusc also has no eyes, no osphradium (taste organ), and no sensory tentacles for touch reception. It was formerly considered to be closely related to the bivalves based on a bi-lobed shell, bi-lobed mantle and reduced head --features which are more clearly shown in the embryonic form (Morton, 1960). However, modern research suggests that it is more likely descended from a common ancestor of the cephalopods (Palaeos, 2008).