Would it be the Yellow Aztec Marigold (Tagetes Erecta) aka African Marigold.

Don't know about the spidery petals unless it would be T. Erecta "Lemon Mum"

Here is a link that might be useful: Tagetes Erecta

I took a look at where I buy my marigold seeds from. I don't want a bunch of volunteers, but I plant them around my vegetable garden and especially near my tomatoes. They put some kind of chemical into the soil that kills nematodes and also attract beneficial insects, like ladybugs, which will devour aphids. Anyway, it looks like it may have been some kind of African Marigold. They tend to have larger blossoms than the French Marigolds and some of them look quite similar to a chrysanthemum, though I didn't see any that looked particularly 'spidery'. I hope this points you in the right direction :)

Here is a link that might be useful: Photos of marigolds

Thanks, folks. I think D.i.b. may have identified my long-lost plant. In any case, it's the closest I've come. Now will look for some seeds for next season.

Gary