GENERA starting with "D"

Symmetrical biraphid - Decussata valves are linear to linear-lanceolate, with slightly rostrate ends. The striae are punctate, comprised of evident areolae which cross at an oblique angle, forming a characteristic "X" pattern. Decussata includes two species, including the former Navicula placenta. Decussata placenta grows in low nutrient, slightly acidic seeps in Iowa. It is also known from moss and aerophilic habitats.

Asymmetrical biraphid - Delicata valves are slightly asymmetrical to the apical axis and symmetrical to the transpical axis. The valve shape is narrow and lanceolate. The raphe is distinctly lateral and becomes reverse-lateral at the proximal ends. The terminus of the raphe is thin, comma shaped, and terminal raphe fissures are deflected toward the dorsal side. Valves lack a distinct central area. Stigmata are absent. The striae are fine and...

Nitzschioid - The raphe system of each valve is positioned diagonally opposite to one another, demonstrating nitzschiod symmetry. The raphe system is located within a wide, low keel. The raphe may or may not have proximal raphe ends or be continuous across the valve, a feature difficult to see without SEM. Thick internal bars of silica (fibulae) are present and parallel to the striae. The fibulae widen near the valve margins to to...

Symmetrical biraphid - Diadesmis is biraphid, although the raphe often becomes secondarily filled with silica. Frustules of Diadesmis are small, usually less than 30 µm in length. The striae are composed of areolae elongated in the transapical direction, a characteristic that may be difficult to discern in the LM. Frustules form band-like colonies, which may be linked by marginal spines. The raphe systems of many frustules are secondarily...

Araphid - The genus Diatoma possesses characteristic thickened transverse costae, septae are absent. Each valve has a single rimoportula, positioned near a valve terminus and oriented transapically. The phylogenetic relationships within the genus have been investigated (Williams 1985) and two subgenera are currently recognized. Subgenus Diatoma: The striae of the subgenus are comprised of uniseriate rows. Internal transapical...

Symmetrical biraphid - The frustules of Diatomella are symmetrical to the apical and transapical axes. The valve outline is linear-elliptical. An internal septum is present, with three openings forming a distinctive internal thickening of silica. The striae are short, often not extending far beyond the valve margin. The proximal raphe ends are expanded. Diatomella is the only naviculoid diatom that possesses a septum (rather than a...

Asymmetrical biraphid - Frustules of Didymosphenia are asymmetrical to the transapical axis and symmetrical to the apical axis (although some populations may be slightly to strongly asymmetrical to the apical axis). One to several stigmata are present, a feature that may be variable within a given species. A large apical porefield is present at the footpole. The terminal raphe fissures are deflected prior to reaching the apical porefield....

Symmetrical biraphid - Frustules of Diploneis are typically elliptical to panduriform, with bluntly rounded apices. Each valve possesses two longitudinal canals, one on each side of the raphe. The canals are positioned within the silica cell wall and open to the exterior through pores, but lack openings to the interior of the cell. The function of these canals is uncertain. The frustules are heavily silicified, with complex (loculate) areolae....

Araphid - The genus Diprora is monotypic (contains a single species) and, to date, is known only from the state of Hawai'i. The genus is tentatively placed in the Fragilariophyceae, although the relation of Diprora to other related taxa is uncertain. This taxon is somewhat similar to the marine taxon, Hyalinella, although Diprora lacks an ocellus-like structure. The filamentous araphid morphology suggests an affinity to the...

Centric - Discostella grows as solitary cells or forms colonies in chains. The central area may be flat or concentrically undulate. Large, distinctive alveoli from a star-shaped pattern in the central valve. Radial costae are present at the valve margin. Small spines may be present or absent on the costae. Central to the costae are striae, which may be uniseriate or multiseriate. Marginal fultoportulae are present, located on...

Araphid - Frustules of Distrionella are elongated with capitate ends. Valves may be slightly asymmetrical to the transapical axis. Striae are unevenly spaced and become scattered and more irregular at the valve ends. Transapical ribs often evident. A central sternum is absent. Porefields, composed of simple porelli, are present at both valve ends. One rimoportula is present, and is usually positioned centrally within a stria near...