acritarch

[ak-ri-tahrk]
noun Paleontology.
  1. any of various microfossils, of unknown biological affinities, having a central cavity enclosed by a wall of chiefly organic composition.

Origin of acritarch

1963; < New Latin Acritarcha (neuter plural), irregular < Greek ákrit(os) confused, doubtful (see a-6, critic) + archḗ beginning, origin (cf. archi-)
Related formsac·ri·tar·chous, adjective
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018