The Yashica SLR bodies can easiest be sorted with looking at the connector – it all starts with the Y-Bayonet, which only was used very shortly, continues with the popular M42 thread mount and C/Y (Contax/Yashica) bayonet and end with the, again proprietary, Y/AF bayonet which was used in the not very succesfull autofocus series.
A specialty is the 4th species of Yashica SLRs, the Samurai series, a visionary camera with a fixed zoom lens, half-format (meaning the used of 1 standard 35mm negative (or slide) for 2 pictures, and one-hand operation. If you get to see a Samurai today you will rather think of a video camera than a SLR.
Despite the fact that the Samurai series again was not succesful (it might have been a too revolutionary approach at that time) Yashica can be proud of having invented the so-called “Bridge Camera”. Another special feature (due to the one-hand operation concept) is the existance of left-handed models of some Samurai models.
The later Samurai 4000iX (which you can see on 3-2-1 quite often) is neither a SLR, nor is it using half-format – it’s simply just another compact APS camera.