B2620 PTO questions

[Kanook]

Forgive me for a slight tangent, but what is the need for a PTO clutch on some models and not on others? I assume the tractor is an HST? There is no clutch on mine, just a PTO lever. Is this just a 20 series feature?

My understanding is the new B's use a hydraulically coupled PTO....no mechanical clutch....Well the B2650/3350 HST units.