Mallomonas lusca sp. nov. (Synurales, Chrysophyceae)—a rare species from Southeast Asia

A new species of tropical chrysophyte algae, Mallomonas lusca sp. nov. is described from Vietnam based on silica-scale morphology observed using scanning and transmission electron microscopy. Scales of this species were previously found in Malaysia, but had not yet been described. Mallomonas lusca belongs to section Torquatae and is most similar to M. favosa. Its scales have a unique conspicuous rounded pit with a raised thickened central area, which develops in association with the posterior pore in the angle of the posterior submarginal rib. This rounded pit is surrounded by delicate papillae across the border on the shield. Mallomonas lusca has been observed in six localities in Vietnam and one in Malaysia.