(W.Sm.) Ralfs, in Pritchard (1861: 906)
Pinnularia directa W.Sm. (Smith, 1853: 56, pl. 18, fig. 169)
Peragallo (1921: 56), Poulin & Cardinal (1982: 2837, fig. 10), Poulin (1990: 138, pl. 18.1, fig. 24), Hasle & Syvertsen (1997: 280, pl. 63, tab. 70)
Cells solitary, narrowly lanceolate, with acute to slightly rostrate apices; apical axis 53–120 µm; transapical axis 7–12 µm. Transapical striae parallel, uniformly spaced, 7–11 in 10 µm, composed of slit-like poroids. Poroids 30–33 in 10 µm, orientated longitudinally in central part of valve, but obliquely towards the valve apices. Raphe central; central raphe endings expanded into pores; terminal endings hooked in the same direction. Chloroplasts 2, extending the entire length of cell, appressed to the girdle bands.
Coastal waters off Davis Station, East Antarctica; Southern Ocean, 57°35’S 105°46’E, offshore Wilkes Land; Arctic to Antarctic (Poulin, 1990); Ross Sea (Andreoli et al., 1995); coastal waters off Syowa Station, East Antarctica (Ishikawa et al., 2001).
Navicula directa is reputedly a bottom-dwelling species that is found occasionally in the plankton (Hendey, 1964). Navicula directa var. javanica Cleve, which also has an Arctic to Antarctic distribution (Poulin, 1990), differs from the type variety in its larger size (apical axis 86–145 µm; transapical axis 11–12 µm) and valve striation (cross-linear and parallel striae 6–7 in 10 µm).