Strategypage describes the operation and the Spetsnaz who carried it out. Which is still going on in eastern Ukraine, actually.
UPDATE: More from Strategypage:
[Now] we know that in Crimea the 22nd and 45th GRU (Military Intelligence) spetsnaz (special operations) regiments were active early and often. There were only a few hundred of spetsnaz ... wearing uniforms with no insignia. Also identified were members of the infamous (for brutal but effective special operations in Chechnya) Vostok battalion and an airborne unit (31st Airborne Brigade) that has showed up in a lot of tricky situations (Bosnia, Chechnya, Georgia). In other words what foreign intelligence agencies have come to regard as The Usual Suspects whenever there is an operation using a lot of special operations troops.
I wonder if these troops have been shifted to eastern Ukraine? Perhaps there really weren't enough Usual Suspects for simultaneous Russian operations in Crimea and eastern Ukraine.