Let's evaluate each statement with regard to the type of body cavity they describe:

A. Annelids are true coelomates: This statement is correct. Annelids (segmented worms, including earthworms) possess a true coelom, which is a body cavity fully lined with a mesodermal layer more specifically called peritoneum. This allows for the distinction of the internal organs from the body wall, and it facilitates greater complexity and organization of the internal structures.

B. Poriferans are pseudocoelomates: This statement is incorrect. Poriferans (sponges) do not have any type of body cavity. Sponges are at a basic level of complexity and lack true tissues and organs, including a coelom or a pseudocoelom. They are considered to have no body cavity and are thus neither coelomates nor pseudocoelomates.

C. Aschelminthes are acoelomates: This statement is incorrect. Aschelminthes, more commonly referred to as Nematoda or roundworms, are actually pseudocoelomates. They possess a pseudocoelom, which is a body cavity that is not entirely lined by mesodermal tissue, unlike a true coelom. The pseudocoel serves as a rudimentary circulatory system and provides a space for internal organs.

D. Platyhelminthes are pseudocoelomates: This statement is incorrect. Platyhelminthes (flatworms) are acoelomates, meaning they lack any body cavity. Their bodies are solid between the digestive tract and the body wall, lacking a filled cavity that would separate these structures.

From the analysis above, only statement A is accurate:

• A. Annelids are true coelomates - Correct
• B. Poriferans are pseudocoelomates - Incorrect
• C. Aschelminthes are acoelomates - Incorrect
• D. Platyhelminthes are pseudocoelomates - Incorrect

Thus, the correct answer to the question is:

Option B: A only