AIIMS 2019 Zoology Echinodermata MCQ Question

Option A is correct because it includes a water vascular system, which is a characteristic feature of echinoderms (e.g., starfish), and a calcareous shell, which is found in mollusks (e.g., snails). Option B incorrectly pairs a water canal system, which is not a recognized term in this context, with a calcareous shell. Option C mentions acoelomate, which refers to organisms without a body cavity, but both echinoderms and mollusks are coelomates. Option D incorrectly associates pseudocoelomate organisms, which have a body cavity derived from the blastocoel, with a water vascular system, which is specific to echinoderms.