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Diatoms of the United States is now known as Diatoms of North America.
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GENERA starting with "c"


Caloneis 4

  1. Striae chambered
  2. One or two longitudinal lines may be present
  3. Central area may have lunate or irregular thickened areas

Symmetrical biraphid - Species of Caloneis are characterized by chambered striae, like those of Pinnularia. The chambered striae give the appearance of one to two longitudinal lines. The striae of Caloneis are composed of fine alveoli, also like Pinnularia. The central area of Caloneis may be expanded, and may include silica thickenings that are lunate or irregular in shape. Living cells possess one or two plastids. Several species within...

Campylodiscus 1

  1. Valve 'saddle' shaped
  2. Raphe runs along entire valve margin
  3. Raphe positioned in marginal keel

Surirelloid - Frustules of Campylodiscus possess a complicated three-dimensional structure which is often termed a distinctive “saddle shape”. Like the other genera within the family Surirellaceae, the raphe system is raised onto a keel and positioned along the entire valve margin. Cells possess a single chloroplast, with two lobed margins. Cells grow singly in epipelic habitats of freshwaters, brackish waters and marine...

Capartogramma 1

  1. Central region X-shaped
  2. Pseudosepta present
  3. Axial area narrow
  4. Striae uniseriate, punctate

Symmetrical biraphid - Capartogramma is characterized by a very distinctive “x-shaped” thickening of silica near the central part of the valve. Frustules are generally lanceolate in valve outline. Pseudosepta are present at the valve apices. The raphe is positioned within a narrow axial area. Striae are uniseriate and punctate. Capartogramma is monotypic in North America (C. crucicula [Grunow ex Cleve] Ross). This species is found in rivers...

Cavinula 8

  1. Valves linear-lanceolate to nearly circular
  2. Striae uniseriate
  3. Striae radial
  4. Terminal raphe fissures absent

Symmetrical biraphid - Species of Cavinula are characterized by uniseriate, radial striae composed of round to elongate areolae. Valves are linear-lanceolate to nearly circular in outline. Internally, the central sternum is thickened, a feature visible in SEM. Externally, the proximal raphe is expanded, while the internal proximal raphe ends are straight. The terminal raphe fissures are absent. One or two chloroplasts are present in living...

Chaetoceros 1

  1. Frustules with long, thin spines
  2. Spines overlap to form colonies of several cells

Centric - Chaetoceros is a centric diatom with very lightly silicified frustules. Each frustule possesses four long, thin spines, or setae. The setae link the frustules together to form colonies of several cells. Frustules are usually seen in girdle view. Chaetoceros is primarily a marine genus, with only a few representatives in inland waters of the United States. Inland cells reach their greatest abundances in saline or brine...

Chamaepinnularia 2

  1. Striae composed of chamber-like areolae
  2. Externally, areolae covered by vela

Symmetrical biraphid - The valve margins of Chamaepinnularia are linear, nearly linear, or undulate. Cells are small, usually less than 25 µm in length and 4 µm in breadth. The striae are composed of simple, chamber-like areolae, with external openings covered by vela. Internally, the areola openings are divided with internal plates of silica. The raphe system may be simple or complex in structure, as in Pinnularia or Navicula. Externally,...

Cocconeis 6

  1. Frustules heterovalvar - one valve with a raphe, the other lacking a raphe
  2. Valves elliptic
  3. Striae uniseriate in freshwater species
  4. Terminal raphe fissures absent

Monoraphid - Cocconeis is heterovalvar, that is, the raphe valve ornamentation differs from that of the rapheless valve. Ornamentation of the raphe valve may differ markedly from that of the rapheless valve. The valve mantle is narrow in relation to the valve face, so cells are rarely (if ever) seen in girdle view. Valves may be flexed, or arched, along the apical axis forming a ‘saddle’ shape. Striae are often uniseriate, but some...

Cosmioneis 3

  1. Striae uniseriate and radial
  2. Valve face flat, with broad valve mantle
  3. Central area elliptical
  4. Internal proximal raphe ends anchor-shaped
  5. External proximal raphe ends expanded

Symmetrical biraphid - Valves of species in the genus Cosmioneis are lanceolate to elliptical in outline, with capitate to rostrate ends. The valve face is flat, and the valve mantles are relatively broad. Striae are uniseriate and radial, and are composed of round to oval areolae. Striae become irregular near the central area. The axial area is narrow and linear, except at the central area, where the central area is expanded and ellipitical....


  1. Stauros narrow
  2. Frustules constricted in girdle view

Symmetrical biraphid - SPECIES OF CRASPEDOSTAUROS ARE NOT KNOWN TO OCCUR IN NORTH AMERICA Valves of Craspedostauros are linear, with a narrow central stauros. In girdle view, frustules are constricted around the central stauros. Cells often lie in girdle view, because of the deep girdle. Numerous copulae, or girdle bands, are present. Areolae are cribrate. Live cells have two lobed chloroplasts. Species within Craspedostauros were previously...

Craticula 15

  1. Striae parallel, or nearly parallel
  2. Valves lanceolate
  3. Central area small or absent
  4. Distinct internal valves may be present

Symmetrical biraphid - The valves of Craticula are lanceolate. The striae are distinctly parallel, or nearly parallel. The central area is greatly reduced or absenct. The genus is polymorphic, forming different valve morphologies. There are three valve types found for this taxon: vegetative, “heribaudii”, and craticula forms. The three forms are produced as a cellular strategy for surviving conditions such as desiccation (Schmid 1979)....

Ctenophora 1

  1. Valve elongate, linear-lanceolate
  2. Central area a thickened fascia with ghost striae
  3. Rimoportulae present at each pole
  4. Rimoportula positioned diagonally

Araphid - Ctenophora frustules are elongate and linear-lanceolate in valve outline. The central part of the valve has a thickened area, or fascia, with faint, ghost striae. Each pole contains a rimoportula, positioned near the axial area. The rimoportula is positioned diagonally. Living cells grow in tuft-like colonies, attached to surfaces by mucilage pads. The genus is common in brackish waters, including sites that have...

Cyclostephanos 2

  1. Striae fasciculate, extending from valve face to mantle
  2. Costae form 2 branches on mantle
  3. Rimoportulae positioned near mantle

Centric - The striae of Cyclostephanos are organized into bundles, or fascicles, that extend from the valve face onto the mantle. The costae, or thickened ribs, also extend from the valve face to mantle. The costae branch on the valve mantle below the plane of the marginal spines, a key feature of the genus. Marginal rimoportulae are positioned near the spines, if spines are present. The branching costae distinguish this genus...

Cyclotella 5

  1. Valve with differential ornamentation between the central and marginal area
  2. Central area flat to tangentially undulate
  3. Single rimoportula positioned on a costa

Centric - In the genus Cyclotella sensu stricto the rimoportula is positioned on a costa, within the ring of marginal fultoportulae (Alverson et al. 2011). Like the genera Cyclostephanos, Discostella and Lindavia the valve face of Cyclotella has differential ornamentation between the central and marginal areas. The central area of the valve face may be flat to tangentially undulate and smooth to colliculate. Numerous marginal...


  1. Frustules very narrow, elongate, with drawn-out ends
  2. Frustules twisted
  3. Frustules very lightly silicified

Nitzschioid - Cylindrotheca cells are solitary and are characteristically needle-like, thin and elongated in shape. The ends of the cell tend to be drawn out from the center part. The frustules are only lightly silicified. The valves, including the keel and raphe canal, wrap around each other, forming a twisted frustule. As a result of the strong twist of the raphe system, the cells rotate and twirl as they move. The girdle bands are...

Cymatopleura 2

  1. Frustules elliptical to panduriform
  2. Valve face undulate
  3. Raphe positioned in marginal keel

Surirelloid - Cymatopleura cells are generally large in size, often over 200 µm in length. The valves are elliptical to panduriform. Species in Cymatopleura possess characteristic undulations on the valve face. In girdle view, Cymatopleura is distinct because of the undulating valve face. The raphe is located within a shallow keel, positioned along entire valve margin. In living cells a single plastid, composed of two plates is...

Cymbella 31

  1. Valves slightly to strongly asymmetric to the apical axis
  2. Valves symmetric to the transapical axis
  3. Distal raphe ends deflected dorsally
  4. Stigmata, if present, located on the ventral side

Asymmetrical biraphid - The valves of Cymbella are slightly to strongly dorsiventral, or asymmetric to the apical axis. Valves are symmetric to the transapical axis. The terminal raphe fissures are deflected to the dorsal side, an important diagnostic feature. Apical pore fields are present at both poles. Striae are uniseriate. One or more stigmata may be present. If a stigma or stigmata are present, they are located on the ventral side of the...

Cymbellonitzschia 1

  1. Valves slightly to strongly asymmetric to the apical axis
  2. Raphe positioned on ventral margin
  3. Cells small

Nitzschioid - Cymbellonitzschia possesses a raphe on the ventral margin of the valve, similar to the genus Nitzschia. In contrast to Nitzschia, however, the valves of Cymbellonitzschia are slightly to strongly asymmetric to the apical axis. The striae are uniseriate. The cells of Cymbellonitzschia are small. Cymbellonitzschia is an uncommon genus that grows on sand and sediment surfaces.

Cymbopleura 33

  1. Valves slightly asymmetric to apical axis
  2. Valves symmetric to transapical axis
  3. Terminal raphe fissures deflected dorsally
  4. Valves lack stigmata and apical pore fields

Asymmetrical biraphid - Cymbopleura frustules are characteristically large and relatively broad in valve outline. The frustules of Cymbopleura are asymmetric to the apical axis, typically with a convex ventral margin and an even broader convex dorsal margin. The striae are composed of rounded areolae. The proximal raphe ends are expanded, while the terminal raphe fissures are hooked and dorsally deflected. Species within Cymbopleura lack apical...