Echinoderms are fascinating marine animals, and their unique features set them apart from other animal groups. The correct answer is b) marine dwellers, endoskeletons, water vascular system.
Echinoderms, which include starfish, sea urchins, and sea cucumbers, are primarily found in marine environments. They possess an endoskeleton made of calcareous plates, which provides structure and support. Additionally, they have a water vascular system that operates their tube feet, allowing for movement and feeding.
In contrast, option a mentions body symmetry, which isn’t a definitive characteristic on its own, as echinoderms exhibit radial symmetry as adults but have bilateral symmetry during their larval stage. Option c is incomplete as it only refers to bilateral symmetry, which does not apply to adult echinoderms. Thus, option b accurately captures the primary characteristics of these intriguing organisms.