(Adds details on FX liquidity) By Chijioke Ohuocha ABUJA, June 7 (Reuters) - Nigeria"s naira slid past 500 per dollar on the black market on Monday to a more than 3-1/2-year low, two weeks after the country devalued its official exchange rate. Trading volumes fell 14.49% last week to $1.07 billion across the currency markets, data from exchange regulator FMDQ Securities Exchange showed on Monday, citing a decrease in spot market turnover. The central bank in May abandoned its official rate of 380 naira, which it had held since July last year, in an attempt to unify its numerous exchange rates. The naira traded at 412 to the dollar on the spot market on Monday and hit 502 naira on the black market as dollar liquidity declined across the currency markets. Below is a table showing the weekly volumes traded between banks as at June 4, 2021, from the previous week, on Nigeria"s foreign exchange market: Week-ended: June 4, 2021 May 28, 2021 ($ mln) Futures 303.40 190.35 Forwards 89.51 161.20 Spot 676.80 899.42 Total 1,069.71 1,250.97 Source: FMDQ Securities Exchange (Reporting by Chijioke Ohuocha; Editing by Toby Chopra, Kirsten Donovan) Our Standards: The Thomson Reuters Trust Principles.