| Summary: | Abstract: During a survey of the soil diatom flora of the sub-Antarctic Ile de la Possession (Iles Crozet), located in the southern Indian Ocean, an unknown Melosira species was found that could not be identified using the currently available literature on the genus. The species is described as Melosira jeanbertrandiana sp. nov. based on detailed light and scanning electron microscopy observations. The new species is characterized by a relatively high mantle, the presence of several marginal rings of acute, never bifurcating spines and a series of eight rimoportulae near the central area with several others scattered over the rest of the valve face and mantle. The girdle comprising several large, ligulate open copulae and the position of the rimoportulae clearly place this new species within the genus Melosira C.Agardh. The species was observed in bare, moist soil in scratches in cliffs bordering the ocean where the influence of sea spray is obvious. The description of this new species further increases the number of species of the Melosirales compared to other centric freshwater diatoms which are infrequently found on the sub-Antarctic islands.
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