Yes you need a special atomizer for the tank and atomizer setup.
There's the eGo type A and B tank atomizers, which use the type A and B tanks.
The eGo C type A and B atomizers, which use the same tanks.
The 510-T atomizer which uses the 510-T tanks.
The 901-T atomizer which uses the same tanks as the 510.
And the 801-T atomizer and tanks. I've read the 801 tanks are compatible with one of the eGo systems, but I don't know which.
All but the 801 and 901 will work fine on the Riva without an adapter. I used to use the 901 and 510 systems, and the 901 seemed to give better flavor. I've heard the eGo tank systems leaked constantly, but I have no experience with them.