Plesiosaurian clades
From this nested classification for Plesiosauria you can navigate to specific plesiosaur clades (groups). Note that some classifications have placed Rhomaleosauridae outside of Pliosauroidea (=pliosaurs), but I have used a traditional approach and nested Rhomaleosauridae within Pliosauroidea.
Sauropterygian clades
Plesiosaurians (=plesiosaurs) are derived sauropterygians. This nested Sauropterygia classification shows the position of Plesiosauria relative to other major sauropterygian clades.
Redundant sauropterygian clades
‘Nothosauriformes’