Annelids are also known as ringed worms. They are normally found in marine environments and moist soil. They normally reproduce by sexual reproduction but some are able to reproduce asexually or regenerate from severed parts. There are around 17, 000 living species. There are 4 sub groups which are: Polychaetes, Citellates, Oligochaetes and Hirudinea. Some structural features of the Annelids they have long bodies which are segmented externally with ring like constructions called annuli and internally by septa. Each segment contains the same set of organs, a common intestinal tract, circulatory system and nervous system. Their bodies are covered by a cuticle that is secreted by cells. It is made of a tough but flexible collagen. One interesting fact of Polychaetes is that the female produces a light luminescence using their bioluminescent skin to attract the male for mating purposes.