la. Collar away from valve apex, corona present
M. nummuloides C. A. Agardh lb. Collar close to valve apex, corona absent M. arcticas Dickie
M. arctica—northern cold water region (also in the Baltic Sea and in the Oslofjord, Norway). M. nummuloides—cosmopolitan? How to identify: The two species may be identified as whole cells in water mounts. With EM preparations they are also distinguished by the structure of the striae and the labiate process pattern.
Remarks: Formation of resting spores (semiendogenous) is common in M. arctica and not known in M. nummuloides. Melosira nummuloides often appears in coastal plankton, detached from the substratum, and M. arctica and the Baltic form or variety (Syvertsen &c Hasle, 1988) may be just as common attached to sea ice as in the plankton under or in the vicinity of the ice. According to the literature (e.g., Van Heurck, 1909; Manguin, 1960) Melosira is represented in the Antarctic as a tychopelagic species but never abundant. The taxonomy of the Antarctic Melosira species is confusing, and a thorough reexamination is needed.
Genus Paralia Heiberg 1863
Type: Paralia marina (W. Smith) Heiberg.
Basionym: Orthosira marina W. Smith.
s Synonym: Melosira hyperborea Grunow in Van Heurck, 1880-1885, Plate 85, Figs. 3 and 4.
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