The Polychaetes are a type of Annelid that have distinct features that make it clearly different from from other Annelids. It has a very distinct head shape, and has antennas, ears, and even a complete digestive system. Just like most animals, including humans, the Polychaetes have a closed circulatory system, making them unique in that category as well. Oxygen is circulated through the body and throughout blood cells and other organs. Due to its massive size, the Polychaete's blood moves quickly throughout its body compared to other Annelids.