Glycogen is known as animal starch. It is a complex carbohydrate that serves as a form of energy storage in animals, similar to how starch functions in plants. Glycogen is primarily found in the liver and muscles of animals. It is made up of many glucose molecules linked together in a branched structure, making it an efficient way to store and release glucose when needed.

Option 2, cellulose, is a type of carbohydrate found in the cell walls of plants and is not considered animal starch.

Option 3, glucose, is a simple sugar and the primary source of energy for all living organisms. While glucose can be stored as glycogen in animals, glucose itself is not known as animal starch.

Option 4, chitin, is a complex carbohydrate found in the exoskeletons of insects and the cell walls of fungi. It is not considered animal starch.

Therefore, the correct answer is option 1, glycogen.