Phylum Aschelminthes: The Roundworms
Phylum Aschelminthes marks a genuine turning point in the survey of animal diversity. Where the flatworms are dorsoventrally flattened and acoelomate, the roundworms present a cylindrical body with a circular cross-section and a fluid-filled pseudocoel that reorganises the way organs are arranged and supported.
This quiz tests the defining features of the phylum exactly as the syllabus presents them:
- Circular cross-section and the name “roundworms”
- Free-living (aquatic and terrestrial) and parasitic habits
- Organ-system level of organisation and bilateral symmetry
- Triploblastic and pseudocoelomate condition
- Complete alimentary canal with a muscular pharynx
- Excretory tube opening through an excretory pore
- Dioecious sexes, with females often longer than males
Keep the three standard examples in mind as you work: Ascaris (roundworm), Wuchereria (filaria worm) and Ancylostoma (hookworm). Read each question carefully — the distractors are drawn from the neighbouring phyla, so precision matters.
Q1. The members of Phylum Aschelminthes are commonly called roundworms because their body is:
The body of aschelminths is circular in cross-section, and this is precisely why they are called roundworms.
Q2. Which of the following correctly describes the level of body organisation in roundworms?
Roundworms have the organ-system level of body organisation, the most complex grade, in which organs cooperate as integrated systems.
Q3. The body cavity of an aschelminth is best described as:
Aschelminths are pseudocoelomate: a body cavity is present but it is not a true coelom fully lined by mesoderm.
Q4. Which set of features applies to Phylum Aschelminthes?
Roundworms are bilaterally symmetrical, triploblastic and pseudocoelomate animals.
Q5. The alimentary canal of a roundworm is described as complete because it:
A complete alimentary canal has two openings, a mouth and an anus, unlike the blind sac of flatworms.
Q6. In aschelminths, the well-developed muscular structure immediately behind the mouth is the:
The alimentary canal is complete with a well-developed muscular pharynx, which helps in drawing in and pushing along food.
Q7. Body wastes in roundworms are removed from the body cavity through the:
An excretory tube removes body wastes from the body cavity and discharges them through the excretory pore.
Q8. The sexes in Phylum Aschelminthes are described as dioecious, which means:
Dioecious means the sexes are separate, that is, males and females are distinct individuals.
Q9. Regarding body length in roundworms, the syllabus states that:
A standard feature of the phylum is that females are often longer than males.
Q10. Which of the following is NOT an example of Phylum Aschelminthes?
Nereis is an aquatic annelid, whereas Ascaris, Wuchereria and Ancylostoma are the aschelminth examples given in the lesson.
Q11. The habitat range of aschelminths, as described in the lesson, includes:
They may be free-living, aquatic and terrestrial, or parasitic in plants and animals.
Q12. Which example is correctly matched with its common name?
Wuchereria is the filaria worm; Ascaris is the roundworm and Ancylostoma is the hookworm.
Q13. Fertilisation in aschelminths is internal, and development may be:
Fertilisation is internal and development may be direct (young resemble the adult) or indirect.
Q14. Compared with the flatworms of the preceding lesson, the key structural advance in roundworms is:
Roundworms add a pseudocoelom and a digestive tube open at both ends, while segmentation and a true coelom belong to annelids.
Q15. Which statement about the excretory system of roundworms is correct?
The lesson states that an excretory tube removes body wastes from the body cavity through the excretory pore.