Sharks and dogfishes differ from skates and rays by

1. Their pectoral fins distinctly marked off from cyclindrical bodies
2. Gill slits are ventrally placed
3. Head and trunk are widened considerably
4. Distinct demarcation between body and tail

Sharks and dogfishes have cylindrical body while skates and rays have flattened body with winglike pectoral fins which are not distinct from body.