Help!! What are these?!?!

I had the most healthy tank. I started with only five shrimp and had hundreds and I loved it so much and then they all just started dying and I only have four left. the water parameters were great. the temperature was perfect and then today I saw these nasty little worms just hanging out of my skrimp. I’ve had some detritus worms, but I replaced the substrate a while ago and got rid of them all and at this point I just have no clue please help😭🙏🏼