Which Came First, the Snail or the Slug?

I'm glad I'm not a cat because it is said "curiosity killed the cat." Shortly after posting my favorite slug photo yesterday, I came across this one of a garden snail. My mind was flooded with questions as if they arose from some source outside myself. Does the word "snail" sound as exotic to the Frenchman as the word "escargot" apparently does to us? I remember once satisfying the curiosity of my very good physics class in Colorado years ago by preparing escargot over the Bunsen burners in our lab. There was an interesting juxtaposition of odors as the Homemaking Department was next door and they happened to be baking a cake that day. Our different odors were being exchanged through the ventilator system.
My curiosity then switched back to my question of today, Which came first?... We know that snakes evolved from lizards who lost their legs. The fossil record makes that very clear, plus we can find the evidence of lost legs in the boa family in the remnants of a pelvic girdle buried in their hind quarters - although I guess that term no longer applies. We also know that whales evolved from land-dwelling tetrapods. They too have the remnants of a pelvic girdle, among many other bits of evidence. So, I did a little internet research, and, it appears that shells have come and gone a number of times in the history of gastropods. Today, not only do gastropod shells come in all shapes and sizes, but there are borderline species with very tiny visible shells or shells buried beneath the skin so they outwardly resemble slugs. A fascinating feature of the snails with exposed spiral shells is that most are right-handed (dextral) while others are left-handed (sinistral). That brings to mind the association of dextrous with dextral and sinister with sinistral, but don't get me started....
I almost forgot why I included the photo of the tiny frog in this discussion. What struck me is that this tiny vertebrate with its complete anatomy that includes virtually all of the organs we humans have is smaller than one digit of the person holding it! Makes me ponder the relative sizes of things - giant beetles and grasshoppers vs. very tiny fish and amphibians. I have memories of seeing a very large frog eat a very tiny bird, a small mammal, and a golf ball. In the case of the latter, I gently pushed the lump in his stomach forward to relieve him of this non-food, then he promptly ate it again! Next time you get a chance to watch a frog swallow, especially a large frog, watch carefully and you will see how it uses its eyes to swallow. Thoughts to explore on another day.