I took a look at the critter identification sticky but I can't seem to find this guy. Originally spotted by my mom, the "head" was sticking out of the substrate and retracted when I went to grab it. I pulled out an inch and a half grub/worm. It is a quarter inch in diameter. It dug itself back into the substrate rear end first, at least I think that was it's rear end. Anyway here are some pictures, I wish I had gotten better ones. I have noticed the gravel moving from time to time, but I thought it was my assassin snails.
The substrate is fluval stratum, there is some glossosstigma in the background, and dwarf hair grass (for size reference). What is this thing? If it feeds on detritus then I don't care, but if it has an appetite for shrimp/plants then I may remove him from the tank...
After looking though google images, the spiracles (little tentacle things) on the end of the larva match up with the ones in some of the pictures. I would agree with you, it probably is a crane fly larva. Considering they have numerous different species of these things, with some larva being totally aquatic, the crane fly fits the bill.
The girl at the shrimp store says they sometimes get them from moss shipments. I did just add new moss from them.
Thanks! Not being able to ID the thing was really bugging me.