The Genus Thalassiosira: The Bipolar Diatom T. antarctica Comber

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Abstract
T. antarctica Comber was described from the southwest Atlantic, and recent collections from that area have resulted in ten clonal cultures. The species has a disjunct geographical population in the north Atlantic, and 2 clonal cultures from Oslofjord [Norway] were grown for comparison. The fine structure of the vegetative frustules of the two populations appear to form a continuum. Resting spores have been formed in senescent cultures, and there are marked differences in the morphology of the resting spore values of the 2 disjunct populations, showing some genetic separation; the northern population is thus called T. antarctica var. borealis, var. nov. Resting spore formation results from a determinate number of divisions giving rise 2-4 resting spores per vegetative cell, with the final nuclear divisions unequal and the 2 depauperate vegetative thecae cast off with rudimentary valves.