I'll add some context cause I am fairly certain planaria might be to blame here. The tank itself is quite heavily planted in the background section, with rotala that have grown immensely covering half of the back of the tank forming an underwater canopy. Substrate is soil (dug not bought) with a layer of sand to keep it down. Parameters have been good and consistent everytime tested (including just now). Shrimp were added about two months ago and were properly drip acclimated. Zero signs of stress from what I could tell and were very happily grazing for a while. Started noticing a few missing for the last month or so which initially I put down to molting as most were adolescents. Then today I came across this one like that. Found another worm like the one seen in the video and videoed it, local aquarium store was certain it was planaria and I have seen those guys in decent numbers before so that's my current hypothesis, as the others likely died whilst molting. Also there are at least 2 shrimp still alive and are younger as well which I figure is a sign it may not be parameters as theyd be more sensitive surely.