Which of the following represents the correct combination without any exception?

Question

Accepted Answer

D. 1. **Checking option A:**
Cyclostomes do have a jawless, sucking circular mouth and lack scales, but they actually possess **unpaired**, not paired, fin-like appendages, making this combination inaccurate.
So, option A is **incorrect**.

2. **Checking option B:**
Birds do have feathers and wings, but their **skin is dry**, not moist and glandular (except for a single oil gland near the tail base), so this description doesn't fully match.
So, option B is **incorrect**.

3. **Checking option C:**
Mammals generally have mammary glands, hair, and pinnae, but aquatic mammals (like whales) and egg-laying mammals (like the platypus) often **lack external pinnae**, so this isn't true without exception.
So, option C is **incorrect**.

4. **Checking option D:**
Class Chondrichthyes (like sharks and rays) consistently show a ventrally placed mouth, gills without an operculum covering, tough placoid scales on the skin, and a notochord that persists throughout life — all true without known exception in this class.
So, option D is **correct**.

5. **Conclusion:**
Only option D holds true universally for its group.
Hence, the answer is **option D**.