acritarch

noun

ac·​ri·​tarch ˈa-kri-ˌtärk 

: any of a group of fossil one-celled marine planktonic organisms of uncertain and possibly various taxonomic affinities held to represent the earliest known eukaryotes

Word History

Etymology

Greek ákritos "confused, uncertain" (from a- a- entry 2 + kritós, verbal adjective of krī́nein "to separate, decide") + archḗ "beginning" — more at certain entry 1, arch- entry 1

First Known Use

1963, in the meaning defined above