Just curious.......

[Felinepeachy]

.....about what this was.

 

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[Harry Pristis]

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

Imagine something like this:

​

 

[Exnihilo]

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

 

[Solius Symbiosus]

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.