It actually is a tuba, with the same length of tubing to preserve the pitch (this one is pitched in Eb, but many are pitched in Bb), but its distinctive shape was developed about 100 years ago to be carried in a marching band. Heavy brute, though!
No "octave key." It's not like a woodwind. Brass instruments require you to develop your embouchure. Range of this beauty can be close to three octaves, depending on the player, but two is easily possible for most.