The
Echiura, or spoon worms, are a small group of
marine animals. They are considered a group of
annelids, though they lack the segmented structure found in other members of that group, and are often treated as a separate phylum. The Echiura
fossilize poorly and the earliest known specimen in
Pennsylvanian (called the upper
Carboniferous outside North America). However, U shaped fossil burrows have been found that could be Echiuran date back to the
Cambrian.