Molecular and morphological characterization of three novel Minorisa species (Chlorarachnea) and proposal for an emended description of the Minorisa minuta

Minorisa is a group of tiny uniflagellates belonging to the Cercozoa. These flagellates are the closest heterotrophic relatives of photosynthetic chlorarachniophytes and are one of the most abundant bacterivorous eukaryotes in coastal marine environments. Despite their evolutionary and ecological importance, taxonomic studies on Minorisa have not been conducted since the original description. In the present study, we isolated five Minorisa strains and performed molecular phylogenetic and microscopic analyses. Molecular phylogenetic analysis using small subunit ribosomal RNA gene sequences indicated that the strains form four different subclades in Minorisa. Microscopic observations revealed that these Minorisa strains possess an amoeboid stage that lacks a flagellum. In the amoeboid stage, cells possess lobose and/or extrusive pseudopodia. Based on the phylogenetic analysis and morphological observations, we revised the description of Minorisa and described the following three novel Minorisa species: Minorisa fusiformis sp. nov., Minorisa magna sp. nov. and Minorisa megafusiformis sp. nov.