Worms are in a very broad category that is not officially classified in any scientific sense. While most worms are limbless invertebrates, some worms are actually reptiles or amphibians. Many other animals called worms are simply insect larvae that have yet to metamorphose into their adult stage.
In an attempt to organize different types of worms, three broad classifications have been created. Several different species of worms are included in each group, but all have some similar qualities. The following are the three classifications:
- Annelida – This group is probably the most recognized of the three worm classifications. Phylum Annelida includes some sea worms, but it is mostly comprised of segmented worms such as earthworms. Earthworms are also an unofficial broad classification of worms. Hundreds of different worm species in 16 families are considered earthworms. Earthworms are also divided into three subcategories depending on their ecosystem. Epigeic earthworms live aboveground. Endogeic earthworms live underground but near the surface. Anecic earthworms live deep underground.
- Nematoda – This phylum of worms includes roundworms, hookworms and threadworms. Many roundworms are parasites and can cause a variety of problems for people and pets. Threadworms live on the ground in damp soil, mossy areas or in decaying vegetation. They can also be found in freshwater and saltwater. Hookworms are also parasites. These worms live in the intestines of animals and steal the nutrients from their food before it can be absorbed.
- Platyhelminthes – The worms in this group are flat or ribbon-shaped. Some may also be flat and shaped like a leaf. Many of the species included in this group are parasites, such as tapeworms. Flatworms are another example of worms in this group. These are leaf-shaped and come in nearly as many different shapes and sizes as real leaves.
Because there are so many different species of worms, they are usually grouped together by Phylum. Some common Phyla of worms are as follows:
- Inchworms of Phylum Arthropoda
- Arrow worms of Phylum Chaetognatha
- Ribbonworms of Phylum Nemertea
- Velvet worms of Phylum Onychophora