Like the others, this phylum has a simpler name which in this case is ringed worms. A common ringed worm contains multiple segments that each have their own set of organs and a pair of feet-like structure, which can be used to help it move. These segments are usually separated by a septa, but an anelida can have poorly-defined to no septa. The ones tht do have a well-defined septa each segment is almost like their own living organism. The septa allows the ringed worm to manipulate the size of each segment.
A cross section of an Annelida.
This class mainly lives in an underwater habitat. They have fleshy potrusion called parapodia that have bristles (chaetae), which is why they are sometimes called bristle worms. There are more than 10,000 species in this class such as the clam worm and sandworm. They have many variations as they can live in the coldest ocean or live near the extremely hot hydrothermal vents. Thye grow up to about 10cm, but can be as small as 1mm or as long as 3m. Polychaetes are usually brightly colored and iridescenr. Only less than 2 % of all polychaetes are known to live in freshwaters.
Earthworm on the ground
This class is more commonly known as earthworms. They have a clitellum, which is the bulge that forms during the reproductive part of their life cycle. There are around 8,000 species of clitellatas. They do not have parapodia and their heads are less developed unlike the polychaete. They can live on land, freshwater, or the ocean.
Annelids have circular muscles around their body. These muscle helps them move by making waves of contraction that go throughout the body so that the annelid can push itselves forward.