Question

Sharks and Dog fishes differ from skates and rays because
A. Gill slits are ventrally placed
B. head and trunk are widened considerably
C. Distinct demarcation between body and tail
D. their pectoral fins distinctly marked off from cylindrical bodies.

Answer 1

Hint: Beam, sharks, and skates have a place with class Chondrichthyes. In Greek, Chondrichthyes signifies "ligament" and ichthus signifies "fish." Certain attributes which characterize Chondrichthyes incorporate skeletons made out of ligament, jaws, combined balances, and placoid scales.

Complete answer:
Sharks have a pectoral blade behind the head on one or the other side of its body. These are frequently stretched and are utilized to hold the shark back from sinking to the lower part of the sea, just as for controlling the fish. The shark's balances are inflexible and prolonged. They are upheld via cartilaginous, non-fragmented bars called ceratotrichia. This strength and unbending nature causes the creature to move quickly and with spryness, especially helpful when in quest for prey that darts away. Beams have levelled circles like bodies with five gill leave openings and their mouths commonly situated on their underside. They have enormous pectoral blades, which they move like wings to go in the water, and their tails are for the most part long and slim, with numerous species having at least one sharp, venomous spine that can be utilized to perpetrate agonizing injuries.

Additional information:
Variations for Chondrichthyes incorporate skeletons made out of ligament, jaws, matched blades, and placoid scales The heterocercal tail implies that one flap is bigger than the other and is an augmentation of the vertebral segment. The spine likewise reaches out into the upper fork of the caudal blade. Sturgeon tails are heterocercal, which means the upper projection of the tail is any longer than the lower flap.

So the correct answer is their pectoral fins distinctly marked off from cylindrical bodies.

Note:
They should swim continuously as they come up short on a gas filled bladder for lightness like fish. They additionally need to swim to breath. When resting, sharks siphon water over their gills, and water is taken through the mouth. Benefits to having a ligament skeleton incorporate adaptability, weight decrease, and the capacity to swim quickly in the water