Annelida
The Annelids are a large phylum of segmented worms. There are over 17,000 modern species including ragworms, earthworms, and leeches. They are mostly found in marine environments and moist terrestrial environments. They are bilaterally symmetrical, triploblastic, coelomate organisms. The basic annelid form consists of two segments, each of which has the same sets of organs and, in most polychaetes, a pair of parapodia that many species use for locomotion.
Excretory System
Annelids have strange excretory systems. Annelids with blood vessels use metanephridia to remove soluble waste products, while those without use protonephredia. Both of these systems use a two-stage filtration process, in which fluid and waste products are first extracted and these are filtered again to re-absorb any re-usable materials while dumping toxic and spent materials as urine. The difference is that protonephridia combine both filtration stages in the same organ, while metanephridia perform only the second filtration and rely on other mechanisms for the first. In annelids special filter cells in the walls of the blood vessels let fluids and other small molecules pass into the coelomic fluid, where it circulates to the metanephridia
Examples
Lamellibrachia tube worms have no gut and gain nutrients from chemoautotrophic bacteria living inside them.
Earthworms (Lumbricina) are the most commonly known species of Annelids.
Leeches (Hirudinea) are another type of Annelid.