Consider the following statements :

A. Annelids are true coelomates

B. Poriferans are pseudocoelomates

C. Aschelminthes are acoelomates

D. Platyhelminthes are pseudocoelomates

Choose the correct answer from the options given below :

The correct option is A only.

Let us analyze each statement step-by-step based on the classification of animals according to the presence or absence of a body cavity (coelom):

1. Understanding the types of body cavity (coelom):
- Coelomates (True coelomates): Animals possessing a true body cavity (coelom) which is lined by mesoderm on all sides. Examples include Annelids, Molluscs, Arthropods, Echinoderms, Hemichordates, and Chordates.
- Pseudocoelomates: Animals in which the body cavity is not completely lined by mesoderm; instead, the mesoderm is present as scattered pouches between the ectoderm and endoderm. The representative phylum is Aschelminthes (roundworms).
- Acoelomates: Animals that completely lack a body cavity. The space between the body wall and gut wall is filled with parenchymal tissue. Examples include Poriferans, Coelenterates, Ctenophores, and Platyhelminthes.

2. Evaluating the given statements:
- Statement A: Annelids are true coelomates.
This statement is correct. Annelids (like earthworms and leeches) are the first evolutionary phylum to possess a true coelom lined by mesodermal epithelium.
- Statement B: Poriferans are pseudocoelomates.
This statement is incorrect. Poriferans (sponges) are cellular-level organisms and do not possess any coelom (they are acoelomate).
- Statement C: Aschelminthes are acoelomates.
This statement is incorrect. Aschelminthes (roundworms) are characterized by having a false coelom, making them pseudocoelomates.
- Statement D: Platyhelminthes are pseudocoelomates.
This statement is incorrect. Platyhelminthes (flatworms) are triploblastic but lack a body cavity, meaning they are acoelomates.

Therefore, only statement A is correct, making A only the correct answer choice.