Hydrocytium expands the phylogenetic, morphological, and genomic diversity of the poorly known green algal order Chaetopeltidales: Conclusions.

The characterization of the strain SAG 40.91 and a critical literature review led us to reinstate the forgotten genus Hydrocytium A.Braun 1855, with SAG 40.91 representing its type species Hydrocytium acuminatum. Independent molecular markers converged on placing H. acuminatum as a deeply diverged lineage of the order Chaetopeltidales, formalized as the new family Hydrocytiaceae. Both chloroplast and mitochondrial genomes shared characteristics with other members of Chaetopeltidales and were bloated by repetitive sequences. Notably, independently of Volvocales the mitochondrial cox2a gene was transferred into the nuclear genome in the H. acuminatum lineage. The nuclear genome data from H. acuminatum, as well as from another chaetopeltidalean reported by others, revealed endogenized viral sequences corresponding to novel members of the phylum Nucleocytoviricota. This article is protected by copyright. All rights reserved.