Aethocrinus

Aethocrinus is an early-diverging crinoid reported from the Early Ordovician.^[1] Its five arms bifurcate.

Aethocrinus Temporal range: Lower Ordovician PreꞒ Ꞓ O S D C P T J K Pg N
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Echinodermata
Class:	Crinoidea
Family:	†Aethocrinidae
Genus:	†Aethocrinus

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.

References

1. Philip, G. M.; Strimple, H. L. (1971). "An Interpretation of the Crinoid Aethocrinus moorei Ubaghs". Journal of Paleontology. 45 (3): 491–493. JSTOR 1302696.