Saving tomato seed - black spots?

[Thelma Sanders]

Some of the seeds I wanted to save had a black dot on them, like frog spawn, something I've never seen before.
Does anyone know what this is?

I've binned all the spotty seeds, but wondered if it was really necessary, as the tomatoes themselves and the plants look healthy. I just didn't want to pass anything nasty on through seed swapping

It's a puzzle

[Bren In Pots]

I've never noticed them on my seeds before either Thelma.