Abstract
Mallomonas spinosa sp. nov. is described from Vietnam. This species has domeless scales with unique four-edged spines, and which are ornamented with papillae. Mallomonas spinosa belongs to the section Papillosae. The morphological characteristics of the scales of the new species are documented by scanning electron micrographs and discussed in detail, including a comparison with related species in the genus Mallomonas.