UPSC Prelims 2003 Q91: Science & Technology – Biology
Octopus is
- (a) an arthropod
- (b) an echinoderm
- (c) a hemichordate
- (d) a mollusc
Answer: (d) a mollusc
Explanation
Classification of the octopus
| Group | Examples |
|---|---|
| Mollusca | Octopus, squid, snail, mussel |
| Arthropoda | Insects, crabs |
| Echinodermata | Starfish, sea urchin |
| Hemichordata | Balanoglossus |
The octopus is a mollusc (class Cephalopoda): it has a soft unsegmented body with a mantle, and no jointed limbs like arthropods or the water vascular system of echinoderms.
Answer: (d) a mollusc.
Why each option is right or wrong
- (a) Incorrect. Arthropods have jointed legs and an exoskeleton.
- (b) Incorrect. Echinoderms are starfish and sea urchins.
- (c) Incorrect. Hemichordates are worm-like, e.g., Balanoglossus.
- (d) CORRECT. The octopus is a cephalopod mollusc.
Key point
Mollusca: soft body, mantle, shell often reduced in cephalopods.
Remember
The octopus is a mollusc of the cephalopod class.
Common mistakes
- Calling the octopus an arthropod because of its eight legs.
- Mixing it up with the starfish of the sea.
- Forgetting the cephalopod class of molluscs.
Exam tip
Octopus, squid, cuttlefish: cephalopod molluscs.
Sources
- NCERT Class XI Biology — Animal Kingdom
- Encyclopaedia Britannica — octopus