The annelids also known as segmented worms, are a large phylum, with over 17,000 species. They have soft bodies with no legs or hard skeleton. Annelid bodies are divided into many little ring-like segments. There are many other kinds of worms, but only annelids are segmented this way. Most marine species are polychaetes (two mostly terrestrial groups are earthworms and leaches). Annelids have bilaterally symmetrical, triploblastic (having three layers of flesh--ectoderm, mesoderm, and endoderm),; they have an internal body cavity with a mouth and anus), invertebrate organisms. They also have parapodia used for locomotion. Many species can reproduce sexually and asexually. Polychaetes produce planktonic larvae. Because they are soft-bodied, fossils are rare. Annelids are known from the Cambrian Period.
|Examples of Annelid Worms|
|Figure 15.17. Fireworm||Figure 15.18. Christmas Tree Worms||Figure 15.19. Tubeworms||Figure 15.20. Flatworm|