Mantoniella beaufortii and Mantoniella baffinensis sp. nov. (Mamiellales, Mamiellophyceae), two new green algal species from the high Arctic

Members of the class Mamiellophyceae comprise species that can
dominate picophytoplankton diversity in polar waters. Yet polar species are
often morphologically indistinguishable from temperate species, although
clearly separated by molecular features. Here we examine four Mamiellophyceae
strains from the Canadian Arctic. The 18S rRNA and Internal Transcribed Spacer
2 (ITS2) gene phylogeny place these strains
within the family Mamiellaceae (Mamiellales, Mamiellophyceae) in two
separate clades of the genus Mantoniella.
ITS2 synapomorphies support their placement as two new species, Mantoniella beaufortii and Mantoniella baffinensis. Both species have
round green cells with diameter between 3–5 µm, one long flagellum and a short
reduced flagellum (~1 µm) and are covered by spiderweb-like scales making both
species similar to other Mantoniella species.
Morphologically, M. beaufortii and M. baffinensis are most similar to
the cosmopolitan M. squamata
with only minor differences in scale structure distinguishing them. Screening of global marine
metabarcoding datasets indicates M. beaufortii has only been recorded in seawater
and sea ice samples from the Arctic while no environmental barcode matches M. baffinensis. Like other
Mamiellophyceae genera that have distinct polar and temperate species, the
polar distribution of these new species suggests they are cold or ice-adapted Mantoniella species.