Hemichordata is a phylum of worm-shaped marine deuterostome animals, generally considered the sister group of the echinoderms. They date back to the Lower or Middle Cambrian and include an important class of fossils called graptolites, most of which became extinct in the Carboniferous. The bodies of Hemichordates are divided into three parts, proboscis, collar and trunk. They have open circulatory systems and a complete digestive tract but the musculature in their gut is very poorly developed, and food is mostly transported through it by using the cilia that cover its inside surface. They have a diverticulum of the foregut called a stomochord,...more »