The sousaphone is known as a marching tuba. It coils around the player with the bell pointing forward. Sousaphones are either made of brass or a white plastic. The difference between sousaphones and tubas is very small. They both play the same notes and use the same valve configuration.
The biggest difference being that the instrument will fit around the body of the musician. This makes it easier to carry it while marching. You can also remove the bell when the instrumenr is put in storage or needs to be transported somewhere.
Thank you, eagle eyed Pbaser for the enlightenment.