This fossil appears to be a Nereidavus invisibilis? scolecodont found in the Silurian Waldron Shale of Clark County, Indiana, USA. The fossil was found on top of another fossil as can be seen in the second picture. The second fossil is a crinoid holdfast.
Thanks to Kenny for the pictures and identification. See other possible scolecodonts found in the Waldron Shale: CLICK HERE and CLICK HERE.
Wikipedia has pictures of the modern sandworm Alitta virens (old genus name Nereis): CLICK HERE
