Q.List the characteristic features that distinguish cartilaginous fishes with living jawless fishes

Cartilaginous fishes are jawed vertebrates with paired fins and placoid scales, whereas living jawless fishes lack jaws, lack paired fins, and lack scales — reflecting their more primitive body plan.

Comparing Class Chondrichthyes (cartilaginous fishes, e.g., sharks, rays, skates) with the living jawless fishes of Superclass Agnatha/Class Cyclostomata (e.g., lampreys, hagfish):

• Jaws: Cartilaginous fishes possess true, movable jaws (they are gnathostomes), allowing active predation/biting. Jawless fishes, as their name states, completely lack jaws; their mouth is a simple round, sucking/rasping structure.
• Paired fins: Cartilaginous fishes have well-developed paired pectoral and pelvic fins. Jawless fishes lack paired fins entirely; they have only median (unpaired) fins.
• Body covering: Cartilaginous fishes are covered with placoid scales (small, tooth-like dermal scales). Jawless fishes have smooth, naked (scaleless) skin, often covered in mucus.
• Gill openings: Cartilaginous fishes typically have 5-7 pairs of exposed gill slits opening directly to the exterior. Jawless fishes have a series of gill pouches (round gill openings/pores, sometimes more numerous, e.g., up to 14-15 pairs in some hagfish). …