Platydemus manokwari isn't dangerous to humans. Not directly, anyway. But it also isn't pretty: The very flat worm grows to about two inches long, and has a murky olive back and a pale belly -- a belly with a mouth in the middle of it. So it basically looks like a sneeze with eyes.
But while the New Guinea flatworm poses no danger to you, it could harm the ecosystem: The flatworm is known to feast on local snails wherever it lands, even climbing up trees to get to them. When the species showed up in France in 2014, researchers argued that consequences could be dire if the species wasn't eradicated immediately. The species is currently contained to a single hothouse, but hasn’t been eradicated.
But don't think you're safe if you don't have a taste for escargot: Snails -- and earthworms, which the flatworm goes after, if its prey of choice isn't around -- are important members of any ecosystem. Earthworms are important in supporting agriculture, and snails are a major source of food for many animals higher up the food chain. Unless Florida's birds develop a taste for flatworm (which is unlikely, because it reportedly has a taste too astringent to tempt even chickens) we might be in trouble.
The main concern -- both in France and in the United States -- is that New Guinea flatworms have been prolific on islands they've made their way to. It takes them a long time to end up on a new island, because they have to be carried in accidentally in some infested soil or plant matter. But now that the species has landed on large land masses -- like the continents of Europe and North America -- there's no telling how quickly it will be able to spread.