Echiura

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.