Which of the following is a characteristic of mollusc?

Step 1: Analyze the question We need the characteristic that belongs to molluscs (snails, slugs, mussels, oysters, octopus, squid).

Step 2: Key concepts about molluscs

• Soft, unsegmented bodies, usually covered by a calcareous shell (not a jointed exoskeleton)
• A muscular foot, a mantle, and often a radula
• Triploblastic: the body develops from three germ layers (ectoderm, mesoderm, endoderm), so the body wall has three layers
• Bilateral symmetry, with a coelom that is reduced

Step 3: Check each option

• A. Hard exoskeleton: Arthropods have a hard chitinous exoskeleton. Molluscs have a shell secreted by the mantle, which is not a true exoskeleton in the arthropod sense. Also, some molluscs (slugs, octopus) have no shell. ✗
• B. Segmented bodies: This is a feature of annelids (earthworms) and arthropods. Molluscs are unsegmented. ✗
• C. Body walls have three layers: Molluscs are triploblastic, so this fits. ✓
• D. Paired jointed appendages: This is the defining feature of arthropods. ✗
• E. A pair of antennae on the head: Insects, and crustaceans (which have two pairs), have antennae. Snails have tentacles, which are not the same as arthropod antennae. ✗

Step 4: Answer The correct option is C.

Exam tip: Remember how to separate the phyla:

• Arthropods = jointed legs + exoskeleton + segmentation
• Annelids = segmented worms
• Molluscs = soft, unsegmented body + shell + muscular foot

If you see "jointed" or "segmented," think of arthropods or annelids, not molluscs.