The Echiura, or spoon worms, are a small group of marine animals. Once treated as a separate phylum, they are now universally considered to represent derived annelid worms.The Echiura fossilise poorly and the earliest known specimen is from the Upper Carboniferous (Pennsylvanian). However, U-shaped fossil burrows that could be Echiuran have been found dating back to the Cambrian.Echiurans are marine worms similar in size and habit to sipunculans.