Echiurans

The Echiura, or spoon worms, are a small group of marine animals. They used to be considered to be part of the phylum Annelida, although they lack the segmented structure found in other members of that group, but are now treated as a separate phylum. However, phylogenetic analyses of DNA sequences suggest that echiurans and pogonophorans should be placed within the Annelida. The Echiura fossilise poorly and the earliest known specimen is from the Upper Carboniferous (called the Pennsylvanian in North America). However, U-shaped fossil burrows that could be Echiuran have been found dating back to the Cambrian.