Which of the following represents the correct combination without any exception? (Characteristics – Class)
- Sucking and circular mouth; jaws absent, integument without scales; paired appendages. – Cyclostomata
- Body covered with feathers; skin moist and glandular, forelimbs form wings; lungs with air sacs. – Aves
- Mammary gland; hair on body; pinnae; two pairs of limbs. – Mammalia
- Mouth ventral; gills without operculum; skin with placoid scales; persistent notochord. – Chondrichthyes
Answer
(4) Mouth ventral; gills without operculum; skin with placoid scales; persistent notochord. – Chondrichthyes
Solution
As per NCERT, Chondrichthyes are marine cartilaginous fishes: the mouth is located ventrally, the notochord is persistent throughout life, gill slits are separate and without operculum (gill cover), and the skin is tough, containing minute placoid scales. So option (4) is correct without any exception.
Each of the others has an error or exception: in (1), cyclostomes do have a sucking and circular mouth without jaws and scales, but paired fins (appendages) are absent; in (2), the skin of Aves is dry, without glands except the oil gland at the base of the tail; in (3), some mammals lack pinnae (e.g. whales) and in some the limbs are modified (e.g. flippers).
Answer: (4)