Annelida
The annelids, formally called Annelida, are a large phylum of segmented worms, with over 17,000 modern species including ragworms, earthworms and leeches. They are found in marine environments from tidal zones to hydrothermal vents, in freshwater, and in moist terrestrial environments. There is no single characteristic or feature that distinguishes annelids from other animals, but there are many distinguishing features across the phylum. Most of an annelid's body consists of segments that are practically identical, having the same sets of internal organs and, in some species, appendages. However, the frontmost and rearmost sections are not regarded as true segments as they do not contain the standard sets of organs and do not develop in the same way as the true segments. As may be inferred from the above, annelids do not have skeletal systems, instead using their segmented bodies for structural support.