In which of the following classes is operculum absent?

Correct option is A

Correct Answer: (a) Elasmobranchii
Explanation:
→ Elasmobranchs (sharks, skates, rays) lack an operculum; instead they have gill slits.
→ Usually 5–7 pairs of gill openings are present on the lateral surface.
→ This feature distinguishes them from bony fishes.
Information Booster:
→ Presence of spiracles assists respiration during resting.
→ Cartilaginous skeleton and placoid scales are key traits.
→ Efficient predators with advanced sensory systems.
Additional Information (Other Options):
(b), (c), (d) — All possess operculum or opercular derivatives.