Difflugia australis was first described by Playfair (1918) and has a unique morphotype that distinguishes it from other similar congeners, such as D. bacillariarum Perty, 1849, and Cylindrifflugia elegans (Penard, 1890) n. comb. González-Miguéns et al., 2022 ^[1]. This differentiation is mainly due to the combination of the following features: The shell is broadly ovate, with a rounded dome and convex sides that converge down to a very short distance from the aperture and diverge suddenly into a short rim (collar). Usually, it is more or less asymmetrical, with one side being more dilated than the other. The shell surface is slightly smooth, composed of flat siliceous plates of irregular shape and size, mixed with fine grains, and with microbial spores of comparable forms spread on the shell surface. Particles are often interspersed with a network of organic cement with a unique mesh pattern. One (sometimes two) slanting spine-like posterior end of the shell is variable in form, and the collar is mainly formed by small plates of equal size. The dimensions of the shell are: total shell length 88–106 µm; shell width 53–88 µm; aperture diameter 19–28 µm; collar height 3–6 µm; spine length 3‒23 μm. The size frequency distributions of both total shell length and shell width indicate that it is a size-monomorphic species with low variability ^[2]. It can be found in freshwater and sphagnum, especially in Australia, Argentina, Belgium, and China ^[1][2].