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, which have lost their segmentation. The majority of echiurans live in shallow water, but there are also deep sea forms. More than 230 species have been described. 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.

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, which have lost their segmentation. The majority of echiurans live in shallow water, but there are also deep sea forms. More than 230 species have been described. 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.