Unidentified

Size about 11mm. This animal is a total mystery to me. It has a partly transparent skin and looks like a caterpillar. However, there are two antennae and the animal was definitely eating, digesting and excreting moss. Taxonomically, I am certain that it belongs into the kingdom Animalia. But then it could be any of the worm phyla, especially annelida. It could also be a mollusc, a snail. Last but not least, it could be an arthropod, namely a lepidoptera. The puzzling anatomy part are the tentacles at the front which point into snail. Any hints appreciated.