Just curious.......

.....about what this was.

The cavities appear to be the traces of crinoid columnals (stem sections) that were preserved, then dissolved away.

Imagine something like this:

It could be pentacrinus (or others crinoids from Toarcian) but your find is very uncommon.

It is next to impossible to identify a crinoid from a stem, and to assign a time??? Well...

FWIW, stalked crinoids(other than comulatids) became extinct after the Paleozoic.