Which of the following possesses mammary gland?

Analyze the question: The question asks which animal has mammary glands. Mammary glands are the defining feature of the class Mammalia.

Explain the concept: Mammary glands are milk-producing glands found in female mammals. They feed the young after birth. Other features of mammals include:

• Body hair or fur
• Warm-bloodedness (endothermy)
• Diaphragm for breathing
• External ears (pinna) in most species
• Live birth in most species

Solution: check each option

• A. Dogfish: a cartilaginous fish, a type of small shark. It has gills and no mammary glands.
• B. Whale: it lives in water, but it is a mammal. It breathes with lungs, is warm-blooded, gives birth to live young, and nurses its calves with milk from mammary glands.
• C. Shark: a cartilaginous fish (Chondrichthyes). It has no mammary glands.
• D. Catfish: a bony fish (Osteichthyes). It has no mammary glands.

Answer: The whale is the only mammal in the list, so it is the only one with mammary glands.

Exam tip: Do not judge an animal by where it lives. Whales, dolphins, and porpoises live in water but are mammals, not fish. If you see "mammary gland" in a question, look for the mammal among the options. Remember: "Fish have gills, mammals have milk."