Toward Modern Classification of Eustigmatophytes, Including the Description of Neomonodaceae Fam. Nov. and Three New Genera¹

Abstract

The class Eustigmatophyceae includes mostly coccoid, freshwater algae, although some genera are common in terrestrial habitats and two are primarily marine. The formal classification of the class, developed decades ago, does not fit the diversity and phylogeny of the group as presently known and is in urgent need of revision. This study concerns a clade informally known as the Pseudellipsoidion group of the order Eustigmatales, which was initially known to comprise seven strains with oval to ellipsoidal cells, some bearing a stipe. We examined those strains as well as 10 new ones and obtained 18S rDNA and rbcL gene sequences. The results from phylogenetic analyses of the sequence data were integrated with morphological data of vegetative and motile cells. Monophyly of the Pseudellipsoidion group is supported in both 18S rDNA and rbcL trees. The group is formalized as the new family Neomonodaceae comprising, in addition to Pseudellipsoidion, three newly erected genera. By establishing Neomonodus gen. nov. (with type species Neomonodus ovalis comb. nov.), we finally resolve the intricate taxonomic history of a species originally described as Monodus ovalis and later moved to the genera Characiopsis and Pseudocharaciopsis. Characiopsiella gen. nov. (with the type species Characiopsiella minima comb. nov.) and Munda gen. nov. (with the type species Munda aquilonaris) are established to accommodate additional representatives of the polyphyletic genus Characiopsis. A morphological feature common to all examined Neomonodaceae is the absence of a pyrenoid in the chloroplasts, which discriminates them from other morphologically similar yet unrelated eustigmatophytes (including other Characiopsis‐like species).

Cell wall and organelle modifications during nitrogen starvation in Nannochloropsis oceanica F&M-M24

“…Some variation in frequency of lamellate vesicles in Nannochloropsis was observed also by Suda et al (2002), even if these authors did not assign any physiological explanation to this variation. After Schnepf et al (1996) and Amaral et al (2020), the lamellate vesicles may contain polysaccharides, possibly paramylon-like, but we show here that there is a continuum from lamellate vesicles towards lipid vacuoles, and the transformation of polysaccharides into lipids would require an enzymatic machinery in the vacuole both for catabolism of carbohydrates and for anabolism of lipids. Our data show that lamellate vesicles are more frequent in starved cells in outdoor cultivation, and hence, factors such as nitrogen depletion (related to lipid accumulation) and type of illumination may be involved.…”

Finding needles in a haystack—Extensive diversity in the eustigmatophyceae revealed by community metabarcode analysis targeting the rbcL gene using lineage‐directed primers

“…Five lineage groups of Eustigmatophyceae were detected, which were placed by Amaral et al. (2020a) in the Clade Goniochloridales (Group 1), the genus Paraeustigmatos (Group 2), Neomonodaceae (Group 3), and the Eustigmataceae (Groups 4 and 5). It is difficult to estimate the number of actual species‐level taxa found among the 214 clones, as some of the groups are resolved as continuous grades with low numbers of substitutions.…”

“…New genera and species have recently been added to the class by Amaral et al. (2020a,b), and these additions were not yet reflected in AlgaeBase. Considerable undescribed diversity of the Eustigmatophyceae has been found using culture techniques and those strains await formal taxonomic descriptions (M. W. Fawley and K. P. Fawley, unpub.…”

Monodopsis and Vischeria Genomes Shed New Light on the Biology of Eustigmatophyte Algae

“…Eustigmatophytes (Class Eustigmatophyceae), a lineage in Ochrophyta (Stramenopiles), are single-celled coccoid algae that can be found in freshwater, soil, and marine environments ( Eliáš et al 2017 ). The phylogeny and taxonomy of this group have only been recently clarified ( Fawley et al 2014 , 2015 ; Eliáš et al 2017 ; Ševčíková et al 2019 ; Amaral et al 2020 ). To date, there are around 20 genera and 189 species described according to AlgaeBase ( Guiry MD and Guiry GM 2021 ), although this classification substantially underestimates the actual diversity of the class ( Fawley et al 2021 ).…”