Exploring Cryptic Diversity and Distribution Patterns in the Mallomonas kalinae/rasilis Species Complex with a Description of a New Taxon-Mallomonas furtiva sp. nov.

A complex of closely related Mallomonas taxa belonging to the section Papillosae, M. kalinae Řezáčová and M. rasilis Dürrschmidt, has been studied in detail by molecular and morphometric methods. Our investigations uncovered the existence of a new species found in water bodies in Vietnam, which we describe here as Mallomonas furtiva sp. nov. This taxon is morphologically very similar to M. kalinae, from which it differs by minute, but statistically significant morphological differences on the structure of silica scales. Indeed, the principal component analysis of morphological traits measured on silica scales significantly separates all three species in the complex. Mallomonas kalinae and M. furtiva differ by number of papillae on the shield and the dome, as well as by the scale sizes. Likewise, Mallomonas rasilis and M. furtiva are primarily differentiated by the absence of submarginal anterior ribs on silica scales of the former species. Phylogenetic analyses showed that Mallomonas furtiva is closely related to M. kalinae, with which it formed a highly supported lineage. Distribution patterns of all three studied taxa are further discussed.