British divers Rebecca Gallantree and Alicia Blagg failed to claim Britain a Rio Olympic place on a day World Championship history was made.
The Commonwealth champions needed a top-three finish to secure Team GB a synchronised 3m springboard berth in Brazil, but finished 10th in Russia.
Men featured in synchronised swimming for the first time at a World Championships.
Mixed synchronised diving also made its debut and China won the 10m event.
The Canadian team - which featured Olympic medallist Meaghan Benefeito alongside Vincent Riendeau - were second, with Australia third.
London Olympians Gallantree and Blagg had never won a World Championship medal, but prospects of success were boosted after the pair qualified for their final with the fourth highest score.
However, they could not repeat their form from earlier in the day and will now have to rely on the final qualification event - the Rio World Cup - in early 2016.
China, Canada and Australia claimed the gold, silver and bronze medals respectively and secured their places at next year's Olympics.
"We dropped dives as a team early on and it was frustrating because the other countries then moved so far ahead," Blagg told BBC Sport.
Gallantree added; "We'll re-group from here and hopefully come out with better results in the individual [3m springboard] event."
Synchronised swimming is one of only two Olympic sports - the other being rhythmic gymnastics - which currently has events for women only.
World governing body Fina only approved the inclusion of duet competitions featuring men in late 2014 and although initially viewed with some scepticism - particularly in Russia - it was the hosts who led the way on the opening day.
Alexander Maltsev and Darina Vailtova scored 88.8539 to qualify as the leading pair for Monday's final.
Cirque du Soleil performers Bill May and Kristina Lum-Underwood, of USA, were second with 86.7108, and the Italian team (85.4125) were third.