Small freshwater thalassiosiroid diatoms from Pleistocene sediments of Pingualuit Crater Lake, northern Quebec (Canada), including description of Cyclotella pingualuitii sp nov.

Arctic and sub-arctic lake sediment sequences from the Pleistocene are uncommon due to multiple glacial-interglacial cycles and the associated advances and retreats of Pleistocene ice sheets. Pleistocene strata are preserved in a 9-m-long sediment core recovered from Pingualuit Crater Lake, Nunavik, northern Quebec (Canada). In addition to tychoplanktonic Aulacoseira species, the Pleistocene planktonic flora comprises representatives from the thalassiosiroid genera Cyclotella, Discostella and Puncticulata, of which most species are extant in perennially ice-free sub-arctic and arctic lakes. One Cyclotella species, C. pingualuitii is described as new and is characterized by a small central area, multiple central and scattered marginal fultoportulae with triangular satellite pore covers, a single large submarginal rimoportula and alveolate striae of unequal length. Cyclotella pingualuitii is the most prominent species during the oldest diatom-rich interval (DR3) recovered, which was deposited during the Late Quaternary (29-36 ky bp). This species has not been observed above 400 cm in Pingualuit Crater Lake sediments, or elsewhere in Pleistocene or Holocene sequences or modern collections, and is considered extinct.