leech

I've always been quite fond of the ramshorn snails in my guppy tank and some of them have been around for a few years now, but recently the population just... vanished. On closer inspection, I found a damselfly nymph, which I thought was the root of the problem, then caught it eating these...

Has anyone ever dealt with these before? I posted a topic awhile back trying to figure out an invertebrate I had found in my shrimp tank and was able to find out it was a leech (much to my dismay) Today I was browsing around the internet and found out that the specific one I had was a snail...