Abstract
Fossil microeukaryotes are key elements for understanding ancient ecosystems at microscopic level and improving the knowledge on the diversification of microbial life as a whole. We describe Palaeohypothrix bahiensis gen. et sp. nov., an exceptionally well-preserved Lower Cretaceous (Berriasian-Barremian; 145-125 Mya) amber-entrapped microeukaryote, identified as a spirotrich ciliate. The preservation of structures interpreted as the nuclear apparatus and remains of the ciliature revealed a novel ground plan, not found in modern Spirotrichea, thus representing a putatively extinct higher taxon lineage, viz. the Palaeohypotricha nov. tax. Based on cladistic analysis, the new taxon is hypothesized as phylogenetically related to the Protohypotrichia.