GENERA starting with "N"

Symmetrical biraphid - Valves of Navicula tend to be elliptical to broadly-lanceolate in outline. Valve ends may be capitate, acute, rounded, or not expanded. The central sternum is thickened, and that thickening may be somewhat asymmetric. Pseudosepta may be present, or absent. The raphe is straight and filiform, or lateral in some species. The proximal raphe ends are slightly deflected to one side. The central area may be expanded, but the...

Asymmetrical biraphid - The valve outline is very slightly asymmetric to the apical axis, valves are nearly naviculoid in appearance. The raphe is positioned in a nearly central position on valve. The distal raphe ends are deflected dorsally. Striae are lineate. Valves lack apical pore fields. The genus is more closely allied with Navicula than Cymbella. Navicymbula pusilla, one of the brackish to saline taxa, is found in endorheic lakes of...

Symmetrical biraphid - Neidiomorpha is a recently erected genus closely related to Neidium. In Neidiomorpha, the marginal canals are greatly reduced and are termed "shallow caves". Valves are linear, with central margins constricted. The apices are rostrate. The proximal raphe ends are simple pores, slightly deflected to the primary side. Two plastids are present. While species in the genus Neidium possess distinct canals at the valve...

Symmetrical biraphid - Valves are linear, linear-lanceolate, or linear-elliptic with variously protracted and obtusely rounded apices. A longitudinal, hyaline line runs from apex to apex along each side of the valve, interrupting the striae. Outer raphe branches are filiform. The proximal raphe ends are either straight or deflected to the same side. The proximal raphe ends are not expanded. Distal raphe ends are simply curved, rather than...

Symmetrical biraphid - Neidium valves are linear to linear elliptical. Ends are variable in shape across species and may be rounded, capitate, rostrate or protracted. Longitudinal lines are present, formed by internal canals positioned along the valve margins. The proximal raphe ends are bilaterally deflected or straight. In many species, the distal raphe ends appear to bifurcate, forming an apical flap. Interruptions in the striae, or Voigt...

Nitzschioid - The nitzschoid raphe is positioned eccentrically within a keel which is supported by fibulae. Valves lack a sternum. Within the genus, species have a large range in size, from very small to very large. Nitzschia is a very common genus with a large number of species that are often difficult to identify. Some Nitzschia species reach great abundance in waters high in organic pollution.

Symmetrical biraphid - Species of Nupela are small in size, generally less than 20 µm. Although the genus was first described as being isovalvar, many recently described species have been found to be heterovalvar in regard to raphe development. Heterovalvar species have one valve with a fully developed raphe and the other valve with a reduced, or absent raphe. The valves of Nupela are slightly asymmetric to the apical axis and the central...