Tetramphora guide
Credit: Josh Stepanek and Pat Kociolek
  1. Valve faces in single plane
  2. Striae composed of apically or transapically oriented areolae
  3. Dorsal central area hyaline

Cells are elliptic. Frustules are strongly asymmetric, so that both valve faces lie in the same plane. Valves are moderately to strongly dorsiventral.

The raphe is biarcuate. The proximal raphe ends are ventrally deflected, but they may be obscured by a hyaline area. The hyaline area may give the appearance of dilated to undulate proximal raphe ends. The distal raphe ends are dorsally deflected. Internally, the proximal raphe branches may be continues though the central nodule. The raphe distally terminates in helictoglossae.

The striae are compose of apically or transpically oriented areolae, with slit-like external expression.

Chloroplasts are composed of two pairs of plate-like plastids. One plastid is appressed dorsally, while the other is appressed ventrally. The plastics are joined by large pyrenoids.

The genus Tetramphora was recognized based on morphologic and molecular data (Stephanek and Kociolek 2016). The genus is considered monophyletic, distinct from Amphora, and includes several species previously classified as Amphora (Stephanek and Kociolek 2016). Tetramphora was separated from Amphora based on Mereschkowsky (1903), in particular, type 8 chloroplasts and a distinct central hyaline area that produced the proximal ends of the undulate raphe.

Species within Tetramphora are found in high conductivity inland waters, marine, and brackish habitats.