Testate Amoebae from South Vietnam Waterbodies with the Description of New Species Difflugia vietnamica sp. nov.

Testate amoebae in Vietnam are still poorly investigated. We studied species composition of testate amoebae in 47 waterbodies of South Vietnam provinces including natural lakes, reservoirs, wetlands, rivers, and irrigation channels. A total of 109 species and subspecies belonging to 16 genera, 9 families were identified from 191 samples. Thirty-five species and subspecies were observed in Vietnam for the first time. New species Difflugia vietnamica sp. nov. is described. The most species-rich genera are Difflugia (46 taxa), Arcella (25) and Centropyxis (14). Centropyxis aculeata was the most common species (observed in 68.1% samples). Centropyxis aerophila sphagniсola, Arcella  discoides, Difflugia schurmanni and Lesquereusia modesta were characterised by a frequency of occurrence >20%. Other species were rarer. The species accumulation curve based on the entire dataset of this work was unsaturated and well fitted by equation S =19.46N0.33. Species richness per sample in natural lakes and wetlands were significantly higher than that of rivers (p < 0.001). The result of the Spearman rank test shows weak or statistically insignificant relationships between species richness and water temperature, pH, dissolved oxygen, and electrical conductivity.