who was the russian legislative body in 1917?

The State Duma in 1906 - 1917 became the first Russian Parliament.

The events of late February 1917 are known as the February Revolution. After the overthrow of the emperor, a shaky coalition of conservative, liberal, and moderate socialist politicians declared itself the Provisional Government, on February 27, 1917.

The second revolution was initiated by an armed insurrection on October 24 and 25, 1917. Known as the October Revolution or the Bolshevik Revolution, it was led by a group of revolutionary socialists called Bolsheviks. It swept aside the Provisional Government with the goal of giving “all power to the soviets.”

I'd say the provisional government, the Bolsheviks didn't really take over completely until late October/November and even then they didn't get a proper government body together for a while.