Muscovies, as far as I've been able to tell, are not the same species as ducks.
They can breed with ducks, but the hybrids are sterile. Some of the females can lay eggs, I think if the Muscovy is the mother, but those eggs don't hatch. Around here the 'mule' ducks are very common as they grow quickly, and they are often called 'French Ducks' as they are produced in great numbers for the French Fois Gras industry and the surlpus seem to end up in the Portuguese markets. Their livers apparently have the same tendency to grow hideously in response to force-feeding as a goose's liver does, and they take up less space in the feeding crates.
The ones I've bought in the past have been 'French' ducks, with a Muscovy dad and a 'normal' duck for a mum, and we've never even had one egg from them.
Muscovy Wiki