Aethocrinus

Aethocrinus is an early-diverging crinoid reported from the Early Ordovician. Its five arms bifurcate.

The contested Echmatocrinus  notwithstanding, it is a candidate for the earliest true member of the crinoid class – though not being a member of the crown group, quite where within the stem group to draw the distinction between eocrinoids and crinoids is a somewhat arbitrary decision.