Roundworms are unsegmented worms that have a body cavity called a pseudocoelom partially lined with mesoderm tissue. They have a digestive system with two openings, a mouth and an anus, through which wastes leave. Parasitic roundworms that can infect humans include those that cause trichinosis, filariasis, ascariasis, and hookworm infection.

1. 27-2 Roundworms

2. Pseudocoelom
• Body cavity between the endoderm and
mesoderm tissues that is partially lined with
the mesoderm tissue

3. Anus
• Opening through which wastes leave the
digestive tract.

4. Key Concept
• Roundworms are unsegmented worms that
have pseudocoeloms and digestive systems
with two openings- a mouth and an anus

5. Key Concept
• Parasitic roundworms include trichinosis-
causing, filarial worms, ascarid worms, and
hookworms.