How do cephalochordates feed while buried in marine sediment?

Cephalochordates, commonly known as lancelets, are suspension feeders that typically remain buried in marine substrate with their mouths positioned just above the surface of the sand.1

To feed, they draw a current of water into their mouths using the beating action of cilia located on their gills. To prevent sand and other large debris from entering, the tentacle-like buccal cirri surrounding the mouth form a protective grid. Once inside the pharynx, the water passes through the gill slits, where a sheet of mucus—secreted by the endostyle—traps suspended food particles. This food-rich mucus is then transported to the intestine for digestion. The filtered water continues into the atrium and exits the body through the atriopore.123