KEY CONCEPT Roundworms have bilateral symmetry and shed their outer skeleton to grow.

1. KEY CONCEPTRoundworms have bilateralsymmetry and shed their outer skeleton to grow.

2. Phylum: Nematoda • Unsegmented bodies • May be parasitic or non-parasitic • Inhabits a broad range of environments

3. Roundworms are protostomes with bilateral symmetry. pharynx intestine brain cuticle anus tail Roundworms shed their stiff outerskeleton as they grow.

4. Roundworms have a toughouterskeleton called a cuticle. chitin • made of chitin • must be shed to grow • Roundworms have a pseudocoelom(fluid-filled body cavity), not completely lined by muscle. • Roundworms reproduce sexually.

5. Nearly every plant and animal species are parasitized by roundworms. hookworms pinworms Guinea worms Many roundworms are parasites.

6. Hookworms • Contracted when walking barefoot in contaminatedsoil or sand • Inhabits the intestines of humans and other animals

7. Pinworms • Contracted by unintentionally ingestingeggs • Infest the intestines of humans and lay eggs around the anus

8. Guinea Worms • Contracted from drinkingcontaminated water from ponds or shallow open wells • Migrates under the skin and emerges through the feet

9. “The Worms” Webquest