Hemichordate acorn "worms" (Phylum Hemichordata) burrow deeply in fine, loose, sandy sediments. The casting here is a result of their feeding activities in which they swallow sediments (deposit feeding) then "cast" out the undigested parts in large coiled piles at the surface. They are not true worms, but are related to starfishes and chordates. Similar castings are widespread around the world on sand and mud flats. Dive site "Tanjung Bacatan" or"Playgound" , Lembata, Nera, Indonesia.