  We consider hard three-loop corrections to hyperfine splitting in muonium and
positronium generated by the diagrams with closed electron loops. There are six
gauge-invariant sets of such diagrams that generate corrections of order
$m\alpha^7$. The contributions of these diagrams are calculated for an
arbitrary electron-muon mass ratio without expansion in the small mass ratio.
We obtain the formulae for contributions to hyperfine splitting that in the
case of small mass ratio describe corrections for muonium and in the case of
equal masses describe corrections for positronium. First few terms of the
expansion of hard corrections in the small mass ratio were earlier calculated
for muonium analytically. We check numerically that the new results coincide
with the sum of the known terms of the expansion in the case of small mass
ratio. In the case of equal masses we obtain hard nonlogarithmic corrections of
order $m\alpha^7$ to hyperfine splitting in positronium.
