(Castrac.) Hust. (Grunow) Hasle (1960: 26, fig. 16c, d)
Raphoneis? (Diatoma?) bicuneata Grunow, in Cleve & Möller (1879: nos 208–210)Pseudonitzschia sicula var. bicuneata (Grunow) Perag., in Peragallo & Peragallo (1897–1908: 299, pl. 72, fig. 26)Nematoplata bicuneata (Grunow) Kuntze (1898: 416)See Hasle (1960, 1964) for a more detailed description and additional synonymy.
Hasle (1964: 38, figs 11, 12; pl. 5, fig. 8; pl. 13, fig. 14; pl. 16, fig. 1), Hasle & Syvertsen (1997: 327, pl. 74)
Cells solitary, lanceolate, with somewhat protracted ends in valve view; apical axis 32–39 µm; transapical axis 6 µm. Transapical striae coarse, 8–12 in 10 µm. Interstrial membranes with 2–5 rows of small poroids close to the interstriae. Fibulae 8–12 in 10 µm. Raphe eccentric; central raphe endings terminating in a circular depression. Central nodule present.
Southern Ocean, 57°35’S 105°46’E, offshore Wilkes Land; type locality, Rovingo, Adriatic Sea (Cleve & Möller, 1879); Antarctic BRATEGG stations (Hasle, 1964).
Because their morphology is poorly known, Hasle & Syvertsen (1997) place four varieties of N. sicula within a group “Incertae sedis (Nitzschia)”. Simonsen (1974) noted that this species is highly variable in general (valve) outline. He also observed transitions between var. bicuneata and var. migrans (Cleve) Hasle in his “Meteor ” samples.