Proboscia macintyrei sp. nov. (Bacillariophyceae) from the subarctic Pacific, and new observations on P. eumorpha

Light and scanning electron microscope observations on filtered water samples, collected during the subarctic Pacific cruises of the R/V Vema (VEMA 20; May–July 1964) and R/V Robert D. Conrad (CONRAD 10; June–August 1966), have revealed the presence of two seasonal forms of Proboscia macintyrei sp. nov. The ‘spring’ and ‘winter’ cells of the new species are both solitary (lacking claspers), with the ‘spring’ form possessing a much shorter and more domed proboscis. Proboscia macintyrei usually differs from other living Proboscia species by possessing 1–2 thin, long polar spinulae at the proboscis tip, usually situated on one side, to the left of the longitudinal slit (rimoportula). The proboscis of the P. macintyrei ‘winter’ form normally bears longitudinal crease-like ridges, but without the thinner transverse ribs of P. subarctica. The morphology of these two species suggests they are living representatives of the ‘barboi’ lineage. Proboscia eumorpha is sometimes present on the filters, with the ‘winter’ form being documented herein in detail for the first time.