In addition to the three species given below there is also a subspecies of Western Lowland Gorilla called Cross River Gorilla.

Western Lowland is the smallest

and  Eastern Lowland is the biggest of all the species.

Mountain gorilla has the thickest fur and has a conical head.

All fully grown adult males develop grey hair on theback and are called as 'Silverbacks'.

The main difference between Humans and gorilla's.

The gorilla's have opposing thumbs in both arms and legs. But humans have only opposing thumbs in their arms