Trimastigids are free-living, anaerobic protists that are closely related to the symbiotic oxymonads, forming together the taxon Preaxostyla (Excavata: Metamonada). We isolated fourteen new strains morphologically corresponding to two species assigned to Trimastix (until now the only genus of trimastigids), Trimastix marina and Trimastix pyriformis. Unexpectedly, marine strains of Trimastix marina branch separately from freshwater strains of this morphospecies in SSU rRNA gene trees, and instead form the sister group of all other Preaxostyla. This position is confirmed by three-gene phylogenies. Ultrastructural examination of a marine isolate of Trimastix marina demonstrates a combination of trimastigid-like features (e.g. preaxostyle-like I fibre) and ancestral characters (e.g. absence of thickened flagellar vane margins), consistent with inclusion of marine T. marina within Preaxostyla, but also supporting its distinctiveness from 'freshwater T. marina' and its deep-branching position within Preaxostyla. Since these results indicate paraphyly of Trimastix as currently understood, we transfer the other better-studied trimastigids to Paratrimastix n. gen. and Paratrimastigidae n. fam. The freshwater form previously identified as T. marina is described as Paratrimastix eleionoma n. sp., and Trimastix pyriformis becomes Paratrimastix pyriformis n. comb. Because of its phylogenetic position, 'true' Trimastix is potentially important for understanding the evolution of mitochondrion-related organelles in metamonads.

Department of Biological Sciences University of Arkansas Fayetteville AR 72701 USA

Department of Biology Dalhousie University Halifax B3H 4R2 Canada

Department of Biology Dalhousie University Halifax B3H 4R2 Canada; Yantai Institute of Coastal Zone Research Chinese Academy of Science Yantai 264003 China

Department of Zoology Faculty of Science Charles University Prague Vinicna 7 128 44 Prague 2 Czech Republic

Citace poskytuje Crossref.org

Genomics of Preaxostyla Flagellates Illuminates the Path Towards the Loss of Mitochondria

High quality genome assembly of the amitochondriate eukaryote Monocercomonoides exilis

EukRef-excavates: seven curated SSU ribosomal RNA gene databases

The Oxymonad Genome Displays Canonical Eukaryotic Complexity in the Absence of a Mitochondrion

Fe-S Cluster Assembly in Oxymonads and Related Protists

Fe-S cluster assembly in the supergroup Excavata

Combined morphological and phylogenomic re-examination of malawimonads, a critical taxon for inferring the evolutionary history of eukaryotes

Organelles that illuminate the origins of Trichomonas hydrogenosomes and Giardia mitosomes

Arginine deiminase pathway enzymes: evolutionary history in metamonads and other eukaryotes