The fat that is stored in the abdominal region is classified as

Visceral fat

Explanation:

Visceral fat is one of the types of body fat which is stored in the region of abdominal cavity. The visceral fat is located near several vital organs that are found in the visceral region. Such organs around which the visceral fat is located are liver, stomach and intestines. This fat sometimes also gets build up in the arteries. “Active fat” is a term which is often used for the visceral fat because it actively increases the risk of some serious health problems.

The system of classification relates to the diversity of species because the system of classification is how we organize the diversity of species. With out it we would have a hard time trying to determine which animals belong with which group. There would be no order, just chaos of trying to determine animal likeness of one another. 
To cut this answer short, it helps them organize organisms.