Which pair are pseudocoelomates?

• A. Nematoda and Rotifera
• B. Nematoda and Annelida
• C. Rotifera and Mollusca
• D. Platyhelminthes and Nematoda

Answer: (A)

Pseudocoelomates have a fluid-filled body cavity called a pseudocoel that lies between the gut and the body wall and is only partially lined by mesoderm, not a complete coelom. Nematodes and rotifers share this arrangement, with their cavities formed differently from a true coelom. In contrast, flatworms lack a body cavity entirely (acoelomates), while annelids and mollusks have a true coelom completely lined by mesoderm (eucoelomates). That's why nematodes and rotifers are the pseudocoelomate pair.