What is this alien in my shrimp tank?

Question

The tank is set up since nearly two months now. The shrimp have been in it for around four weeks. One small algae eating fish and one big and accidentally some small snails are living there too. But this strange alien I cannot connect with any of the other. It is around one cm in length and seems to have some kind of spine and a kind of mouth on the spiky end. I imagine some kind of flat worm. I assume it was hiding in some plant, as we bought them...

The important thing: is it dangerous for humans or the life in the aquarium?

Answer 1

I found it is the German "Kleiner Schneckenegel" (Alboglossiphonia heteroclita, synonym: Glossiphonia heteroclita) which is a kind of leech. They eat snails and other related kind of animals. I found the German Wikipedia page but it seems there is no English source for this on Wikipedia. If someone knows a source, I would be happy to add it.

The small snail leech mainly sucks on snails, including those of the genus Lymnaea, which are often suckled by several leeches at the same time. Smaller prey such as worms and insect larvae are also sucked out, usually completely. Therefore, the small snail leech can be classified as a predator.

Snail leeches crawl forward on the ground. They are often very agile and lively.