GEORGETTE DOUWMA / SCIENCE PHOTO LIBRARY GEORGETTE DOUWMA / SCIENCE PHOTO LIBRARY
Acorn worm (order Hemichordata) sand cast. Acorn worms are a type of hemichordate worm that 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. Photographed in the Red Sea, Egypt.
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