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Abstract
Neidium distincte-punctatum was described by Hustedt in 1922 from Lunz Untersee, Austria. Since then, this extant species has been identified from northern Germany, Finland, and Greenland. In North America, N. distincte-punctatum is recorded from the Arctic islands, Alaska, an isolated region in the central United States and Holocene sediments in southern Canada. In this study, data for N. distincte-punctatum is presented from 8 lakes and ponds on Ellesmere Island in the Canadian High Arctic. Valves range in size from 32 to 70 um in length, from 12 to 21 μm in width, and from 12 to 21 μm in depth, with 10-12 striae in 10 μm. There are 11-14 areolae in 10 μm. The morphology of the external valve surface (with large depressions around the areolae) is distinctive for this taxon. The structure of the internal valve surface is unique, with a complex network of braiding silica projections over the areolae. Only one other species, N. boyeri Reimer, is known to have such an internal valve wall structure. This internal valve ornamentation is intermediary between the two contrasting forms of N. holstii (Cleve) Krammer with a costate-like internal surface and N. iridis (Ehrenberg) Pfitzer with a solid internal surface. The linkage between contrasting valve structures is further evidence for the distinctive nature of these species within the genus Neidium while illustrating morphological similarities to Cymbella, Pinnularia and Navicula. On Ellesmere Island, the common species associated with this diatom include Staurosirella pinnata, Staurosira construens, Nitzschia perminuta, Nitzschia sp. [cf. frustulum], and Amphora copulata. Neidium distincte-punctatum is a cold-water (Oligothermal) species with an Arctic polar distribution found in waters of high conductance (salinity) and is tolerant of relatively high levels of sodium and magnesium.
