Which structural feature distinguishes a hard tick (family Ixodidae) from a soft tick (family Argasidae)?
- A Presence of a rigid dorsal scutum covering part or all of the back ✓
- B Presence of four pairs of legs in the adult
- C Absence of hypostome in the mouthparts
- D Absence of spiracles in nymphal stages
Correct answer: A. Presence of a rigid dorsal scutum covering part or all of the back
Explanation
Hard ticks possess a dorsal sclerotised plate, the scutum, which in males covers the whole back and in females only the anterior portion, permitting marked engorgement. Soft ticks lack a scutum and have leathery integument with the capitulum hidden beneath the body. Four pairs of legs are present in adults of both families, and both families possess hypostomes and spiracles, eliminating the other three options.
Reference: Park's Textbook of Preventive and Social Medicine, 26th ed.
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