Home for a largish Hermit Crab - see https://inaturalist.ala.org.au/observations/204245142
My first thought was gastropod but then I remembered otoliths. The latter is possible from what I can see online but I don't think the spiral growth rings fit.
Anyone? ... @rfoster , @ben_travaglini, @mtank, @marinejanine, @streglystendec