Step-by-step explanation:
Bases on the structure of their mouth and the type of the skeleton, scientists have divided the fish into 3 main categories:
- Jawless Fish
 - Cartilaginous Fish
 - Bony Fish
 
Lampreys:
- Lampreys belong to the first category i.e. Jawless Fish.
 - Lampryes are mostly parasites and feed on other fish by sucking their blood and tissues using their suction like mouth structures. 
 - Their body is not covered with scales and they do not have a pair of fins.
 
Skates:
- Skates belongs to the second category i.e. Cartilaginous Fishes. 
 - They have jaws and pair of fine unlike Lampreys (Jawless Fish)
 - Their bodies are covered with scales. 
 - These are carnivores.