Small worm like on dead skeletons

[Boardn365]

I have been having Euphylia die off one at a time for a few months. Have not been able to find out why but one by one they mostly have polyp bailout with a head at a time. I have checked for critters on live heads or the ones that are dying and never seen anything. Last night was doing a water change and moved some dead heads around, I leave them in just in case they want to pop a new baby. I saw these little wormlike critters but they were only on the dead skeletons and only where they were buried in the sand. Wondering if I have some sneaky bad guys.

 

[Uncle99]

Tiny baby Flatworms?
Tons of different species.

 

[Boardn365]

I thought they were bigger. And why would they just be on dead skeletons in buried in the sand