GENERA starting with "r"

 

Reimeria 2

  1. Ventral margin straight to slightly convex
  2. Ventral margin at central area tumid
  3. Stigma single, positioned dorsally in central area

Asymmetrical biraphid - Valves of Reimeria are symmetrical to the transapical axis and asymmetrical to the apical axis. The dorsal margin is slightly arcuate. The ventral margin is markedly expanded, or tumid, at the central area. Apical porefields are present at both poles on the ventral margin and bisected by the terminal raphe ends. The axial area is narrow. A single stigma is positioned on the dorsal side of the central area. Distal raphe...


Rexlowea 1

  1. Septa and pseudosepta present
  2. Valves large
  3. Raphe lateral
  4. Striae near ends biseriate

Symmetrical biraphid - Rexlowea was recently described based on Placoneis navicularis (Ehrenberg) Cox 2003. At present the genus is monotypic. The valves are large (up to approx. 130 ┬Ám in length). The axial area is narrow and straight, with a small central area. The raphe is lateral and undulate. External proximal ends are dilated, while the distal ends are deflected. The striae are radiate. Near the central area, the striae are composed of...


Rhoicosphenia 1

  1. One valve with complete raphe
  2. One valve with small raphe branch (rudimentary raphe)
  3. Pseudosepta at both poles
  4. Frustule curved in girdle view

Asymmetrical biraphid - Frustules of Rhoicosphenia are clavate in valve view and heterovalvar. In girdle view, valves are flexed, and curved. As a result of the asymmetry to the transverse axis, the valve face is curved. One valve has a complete raphe with two distinct raphe branches. The other valve has a very small raphe branch on the footpole. Pseudosepta are present and distinct at both poles. In contrast with species in Gomphonema, valves...


Rhopalodia 2

  1. Symmetry dorsiventral
  2. Raphe positioned in dorsal keel
  3. Valve faces nearly planar

Epithemioid - Frustules of Rhopalodia have a strong dorsiventral symmetry. The raphe is positioned on the dorsal side of each valve in a shallow keel. The valve faces are nearly planar, that is, each frustule is shaped like 1/2 of an orange. The central endings of the raphe are expanded. The raphe is supported internally by costae. In contrast to Epithemia, Rhopalodia lacks complex cingula (girdle bands). Cells of Rhopalodia grow in...


Rossithidium 5

  1. Valve outline linear, lanceolate, sometimes elongate
  2. Striae parallel or nearly so throughout valve length
  3. Axial area narrow

Monoraphid - The valve outline is linear, elongate or lanceolate. The ends of Rossithidium are rounded. The striae are parallel throughout the valve, on both raphe and rapheless valves. The striae are variable and may be uni- or multiseriate. The axial area is narrow. The raphe is straight with expanded proximal raphe ends. Terminal raphe fissures are absent. The central area on the raphe valve varies in both size and shape. Areolae...