All living members of the class Cyclostomata are:

Question

All living members of the class Cyclostomata are:

1. A. Free living
2. B. Endoparasite
3. C. Symbiotic
4. D. Ectoparasite (Correct answer)

Correct Answer

Option D — Ectoparasite

Detailed Solution & Explanation

The correct answer is Ectoparasite.

Key Points

• All living members of the class Cyclostomata (e.g. *Petromyzon*, *Myxine*) are ectoparasites on fishes.
• They are jawless vertebrates that attach to the host's body surface.

Additional Information

• Cyclostomata are the jawless (agnathan) vertebrates — lampreys (*Petromyzon*) and hagfishes (*Myxine*) — with a circular, sucking mouth, no jaws and no paired fins.
• They attach to the body surface of fishes and feed on blood and tissue, which makes them ectoparasites; an endoparasite would live inside the host.
• Other diagnostic features: a cartilaginous endoskeleton, 6–15 pairs of gill slits, a persistent notochord through life, and cyclostome blood is isotonic with sea water — they are marine but migrate to fresh water to spawn, dying afterwards.
• For the NEET chordate sequence, place them correctly: Cyclostomata sits below Chondrichthyes (cartilaginous fishes, jaws present) and Osteichthyes (bony fishes), being the only living jawless class.