Problem 12 - Entrance Test

Let's examine each statement: (A) Echinoderms are indeed exclusively marine, triploblastic (derived from three germ layers), and show organ-system level of organization. This statement is CORRECT. (B) This is a classic characteristic of echinoderms: adults are pentamerous radially symmetrical, while their larval forms (e.g., bipinnaria, brachiolaria) are bilaterally symmetrical. This indicates their evolutionary ancestry from bilateral forms. This statement is CORRECT. (C) The water vascular system (or ambulacral system) is a unique and defining feature of echinoderms, used for locomotion (tube feet), feeding, and gas exchange/excretion. This statement is CORRECT. (D) Echinoderms do possess an endoskeleton of calcareous ossicles (plates). However, they **lack a specialized excretory system** with organs like flame cells. Excretion mostly occurs through the body surface and tube feet. Flame cells are characteristic of Platyhelminthes. Therefore, this statement is INCORRECT.