Title: Worm Phyla: Platyhelminthes, Nematoda and Annelida – Easy Peasy All-in-One High School
Headings: Worm Phyla: Platyhelminthes, Nematoda and Annelida
Worm Phyla: Platyhelminthes, Nematoda and Annelida
The Coelom: An Evolutionary Milestone for Animals
Phylum Platyhelminthes: Flatworms
Phylum Nematoda: Roundworms
Phylum Annelida: Segmented Worms

Content: Phylum Nematoda: Roundworms
Members of the Phylum Nematoda are called roundworms because they are cylindrical in shape, tapered at both ends, and vary in length from being microscopic to 20 inches long. They are covered with a thick protective cuticle that is flexible and can be molted (shed, allowing for growth). Most roundworms are parasites and are found in all habitats. They are bilaterally symmetrical and unsegmented. Roundworms are pseudocoelomates, meaning they having a body cavity that is not completely lined in mesoderm on all sides. The body cavity or pseudocoel serves as a hydrostatic skeleton against which muscles can contract. Unlike flatworms, roundworms have a complete gut. This means that they have a one-way digestive tract with a gut that begins with a mouth and ends with an anus. Therefore, they are usually able to digest food and pass waste in one continuous direction.