Q. Which of the following organisms is not a mollusc? Answer:
Starfish
Notes:
Octopus: Octopuses belong to the class Cephalopoda within Phylum Molluska. Cephalopoda is a group of highly evolved, predatory marine animals. While they share some common ancestors with mollusks, they have distinct characteristics such as a complex nervous system, a beak-like mouth, and tentacles equipped with suckers.
Snail: Snails are indeed mollusks. They are part of the class Gastropoda within the phylum Mollusca. Snails have a coiled shell and a soft body.
Oyster: Oysters are also mollusks. They belong to the class Bivalvia within the phylum Mollusca. Oysters are characterized by their two hinged shells and are known for their filter-feeding lifestyle.
Starfish: Starfish, also known as sea stars, are not mollusks. They belong to the phylum Echinodermata, and they have a completely different body plan and structure compared to mollusks. Starfish have radial symmetry and a unique water vascular system that helps them move and feed.