Quiz: Coelom Quiz
The coelom is one of the quietest yet most decisive features in animal classification. It is not merely a space inside the body — it is a cavity lined by mesoderm, and the presence, nature, or absence of that lining sorts triploblastic animals into three architectural plans.
What this quiz covers
- The definition of the coelom as a body cavity between the body wall and the gut wall, lined by mesoderm.
- Coelomates — annelids, molluscs, arthropods, echinoderms, hemichordates and chordates.
- Pseudocoelomates — mesoderm present as scattered pouches between ectoderm and endoderm, as in aschelminthes.
- Acoelomates — no body cavity at all, as in platyhelminthes.
- Why the presence or absence of this cavity is treated as very important in classification.
Each question is answerable from Lesson 7 alone. Read the options carefully — the difference between a cavity that is lined by mesoderm and one that is not is the whole point of the lesson.
Q1. The body cavity which is lined by mesoderm is called:
The lesson defines the coelom precisely as the body cavity that is lined by mesoderm. A cavity alone is not enough; the mesodermal lining is the operative word.
Q2. Animals possessing a true coelom are called:
Animals possessing a coelom are called coelomates, for example annelids, molluscs, arthropods, echinoderms, hemichordates and chordates.
Q3. In pseudocoelomates, the mesoderm is present as:
In pseudocoelomates the body cavity is not lined by mesoderm; instead the mesoderm persists as scattered pouches in between the ectoderm and endoderm.
Q4. Which of the following is an example of a pseudocoelomate?
The lesson names aschelminthes as the example of pseudocoelomates, in which the mesoderm occurs as scattered pouches.
Q5. Animals in which the body cavity is absent are called:
Animals in which the body cavity is absent are called acoelomates, for example platyhelminthes.
Q6. Which group is given as the example of acoelomates?
Platyhelminthes are the named example of acoelomates, since no body cavity is present in them.
Q7. The presence or absence of a cavity between the body wall and the gut wall is important because it is:
The lesson states directly that the presence or absence of a cavity between the body wall and the gut wall is very important in classification.
Q8. Which of the following is NOT listed as a coelomate in the lesson?
Aschelminthes are pseudocoelomates, not coelomates. Annelids, molluscs, arthropods, echinoderms, hemichordates and chordates are the coelomate examples.
Q9. In a coelomate, the cavity lies:
In a coelomate, mesoderm forms a continuous sheet coating the inner surface of the body wall and the outer surface of the gut, so the cavity sits entirely within mesodermal boundaries.
Q10. The coelom categories (coelomate, pseudocoelomate, acoelomate) apply only to:
The coelom question applies only within the triploblastic set, since a diploblastic animal has no mesoderm to line anything.
Q11. Which of the following correctly pairs an animal group with its coelom status?
Platyhelminthes are acoelomates (no body cavity). Aschelminthes are pseudocoelomates and annelids are coelomates, so the other pairings are wrong.
Q12. A triploblastic animal has mesoderm:
Triploblastic animals are those in which the developing embryo has a third germinal layer, mesoderm, in between the ectoderm and endoderm.
Q13. Which set consists entirely of coelomates as listed in the lesson?
Annelids, molluscs and arthropods are all named coelomates. The other sets each contain aschelminthes or platyhelminthes, which are not coelomates.
Q14. The key feature that distinguishes a coelom from a pseudocoelom is:
Both coelomates and pseudocoelomates possess a cavity between body wall and gut wall; the difference is that in a coelom the cavity is lined by mesoderm, while in a pseudocoelom it is not.
Q15. Which statement about acoelomates is correct?
Acoelomates are animals in which the body cavity is absent, as in platyhelminthes. They are still triploblastic, so they do possess mesoderm.