The Phylum Platyhelminthes has tons of important characteristics. Platyhelminthes is another name for flat worms, they are also very important in the food chain. The flat worm has 3 tissue layers and no body cavity. It shows bilateral symmetry and ceohalization, which means if the head is cut of the correct way it will grow a second one. This Phylum is divided into 3 classes Turbellaria, Trematoda, and Cestoda. Although it has no body cavity it still is acoelomate. Flatworms also have a distinct nervous, digestive, reproductive, and excretory system. This phylum contains parasitic and non parasitic worms. Which can be seen below...


Very different from Platyhelminthes, the phylum Nematoda is roundworms. These worms are known to be long and slender and taper at both ends. These worms have two openings, one being the mouth and the other the anus. The Nematoda have a complete digestive tract and they can be 1mm to 120cm. They can be found living in salt water and fresh water and they are pseudocoelomates. Most are free living but there is also some that are parasitic.


The phylum Annelida is from "annulus" which is Latin for ring and "risks" which is Greek for like. Their body is divided into 3 segments and they have a coelomate body plan with 3 tissue layers. Annelida also have bilateral symmetry. They have 3 classes, Oligochaeta, Polychaet, and Hirudinea. Just like the other phylums, this one also has free living and parasitic worms.