Which lists only coelomate phyla from the provided set?

• A. Annelida, Mollusca, Arthropoda, Echinodermata, Chordata
• B. Porifera, Cnidaria, Platyhelminthes, Nematoda
• C. Annelida, Nematoda
• D. Arthropoda, Echinodermata only

Answer: (A)

Coelomates have a true body cavity, the coelom, that is fully lined by mesoderm. This allows organs to develop and move independently within a well-organized body plan, improving complexity and size. In embryology, the coelom forms within the mesoderm, supporting the idea of a true, enclosed cavity.

From the given set, Annelida, Mollusca, Arthropoda, Echinodermata, and Chordata all possess this genuine coelom. In contrast, Porifera lack a true body cavity and tissues; Cnidaria have a body plan with a simple gastrovascular cavity, not a coelom; Platyhelminthes are acoelomates with no true body cavity; Nematoda have a pseudocoelom, a false cavity not fully lined by mesoderm. Therefore, the only option listing exclusively coelomate phyla is the one that includes Annelida, Mollusca, Arthropoda, Echinodermata, and Chordata.