I agree with FOUND IT, that this is Platydemus manokwari. I've found quite a few in my yard in Austin, Tx. They are usually found near/along with small snails in wet, humid areas. They emit a large amount of a sticky mucus and if you handle them rough they will pull apart into various pieces that will slide/move off in different directions. They do not have the typical anvil shaped head of other planaria I find in the yard or remember from Biology classes, rather a pointy earthworm look. When touched they sometimes shrink up into a flat, wide, fluke or leach looking creature. I researched these guys recently after finding a bunch under wet bricks near my goose pen. I was concerned they could possibly be a parasitic fluke/worm of geese, but they are not. I've read that they are an invasive species, but don't know how damaging they are. I'm over run with snails, so I'm not too concerned yet.