Transfer of the small diatoms Thalassiosira proschkinae and T. spinulata to the genus Minidiscus and their taxonomic re-description

Abstract

The marine diatoms Thalassiosira proschkinae and T. spinulata are relatively small in size; their taxonomic identities have been debated owing to the diverse morphological variations. In the present study, we isolated both morphotypes from Korean coastal waters and examined their fine structures and conducted molecular sequence comparisons. The morphological and molecular analyses showed that T. proschkinae and T. spinulata were certainly distinct, and phenotypic plasticity of valve structure was not noted. Based on the morphological similarity and phylogenetic relationship, we transferred T. proschkinae and T. spinulata to another genus Minidiscus within Thalassiosirales that includes small-sized species and proposed new combination names, Minidiscus proschkinae (Makarova) Park & Lee comb. nov. and Minidiscus spinulatus (Takano) Park & Lee comb. nov., respectively. The genus description of Minidiscus was emended.

Nanoplanktonic diatoms are globally overlooked but play a role in spring blooms and carbon export

“…8c ). A recent study has also transferred two Thalassosira species to the Minidiscus genus after fine structure examination and molecular sequence comparisons 47 , illustrating the difficulty of correct identification in this size-class. These recent changes have been included in the present Tara Oceans data analysis, but do not significantly change the global scale picture.…”

Molecular Phylogeny and Taxonomy of the Genus Minidiscus (Bacillariophyceae), with Description of Mediolabrus gen. nov

“…Minidiscus taxa share the generic characters of having a small cell size and processes more or less concentrated in valve center (Hasle 1973a, Hasle andSyvertsen 1997). The characters guided the identification of new Minidiscus species (Takano 1981, Rivera and Koch 1984, Gao et al 1992, Quiroga and Chr etiennot-Dinet 2004, Park et al 2017, Lyakh and Bedoshvili 2018, and helped isolation and identification of the strains in the present study.…”

“…Minidiscus is distinguished from Thalassiosira and other taxa within the family Thalassiosiraceae primarily by its the small cell size and the processes more or less concentrated in the valve center. The main characters for differentiation among Minidiscus species are areolation and location of the processes (Hasle and Syvertsen 1997, Kaczmarska et al 2009, Park et al 2017.…”

“…inornata, have been described in the complex of M. trioculatus (Kaczmarska et al 2009). Combining morphological and molecular data, two Thalassiosira taxa were recently transferred from Thalassiosira to Minidiscus (i.e., M. proschkinae and M. spinulatus; Park et al 2017). Minidiscus is comprised of 12 taxonomically accepted species (Guiry and Guiry 2020), but for some taxa, the number of records are very limited, some only known from their original descriptions.…”

First record of Thalassiosira catharinensis (Bacillariophyta) from argentinean marine coastal waters.

“…Some of the taxa analyzed in the mentioned literature were transferred to Shionodiscus Alverson, Kang & Theriot in Alverson et al (2006) and Minidiscus Hasle emend Park in Park et al (2017), and most part of them corresponds to the microplankton or to the largest fraction of the nanoplankton. By contrast, the smaller fraction of the nanoplanktonic Thalassiosira species was frequently overlooked.…”