Frustulia inculta

Siver, Pelczar and Hamilton 2009      Category: Symmetrical biraphid

Frustulia esandalliae


Frustulia krammeri

LM scalebar = 10 µm = 40 pixels.


Contributor: Carrie Graeff - March 2012
Length Range: 54-74 µm
Width Range: 11.5-14.0 µm
Striae in 10 µm: 28-30 in the center valve, 27-28 at the ends


Valves rhomboid with slightly constricted apices. The length to breadth ratio is highly variable. Longitudinal ribs and raphe are noticeably curved, giving the species an asymmetric appearance. Longitudinal striae, which are comprised of oval or lanceolate areolae, are present but are very wavy and sometimes disjointed. Striae do not circumradiate the poles. The external raphe ends are T-shaped. Internally, areolae are occluded. The longitudinal ribs and helictoglossae fuse to form a porte-crayon that is somewhat weak in size and shape.

Original Description

Author: Siver, Pelczar, and Hamilton 2009
Length Range: 45-83 µm
Width Range: 10-18 µm
Striae in 10 µm: 28-30

Original Description

Valves are elliptic-lanceolate with shallow mantles and broadly rounded apices (Figs. 51–55 and 60). Striae are parallel over most of the valve face and absent at the poles. The lack of striae around the apices is readily observed with LM (Figs. 57–59). The areolae are not aligned between neighboring striae, forming zig-zagged rows along the apical axis (Figs. 51–59). The axial area and ribs aligning the raphe are bowed or curved between the central nodule and the ends of the valve (Figs. 51–55). The raphe ribs are unevenly fused in the center of the valve forming an asymmetric central nodule (Figs. 56 and 62). The side of the central nodule aligned with the convex side of the axial region is straighter and less swollen than the concave side. As a result, a distinct figure-of-eight design is not formed. The region between the proximal raphe fissures is thickened internally (Figs. 61–62). On the external surface, the central area is not expanded. The helictoglossae are long, linear, and fused at the base with the raphe ribs to form a portae-crayon structure that terminates close to the ends of the valve (Figs. 57–59). The raphe is bowed, filiform, with T-shaped proximal and distal fissures (Figs. 61 and 64). The areolae open externally as circular pores or elongated slits, the latter of which are aligned with the apical axis (Figs. 61, 63, and 64). Internally, the areolae are larger, circular and covered with a slightly raised and perforated hymen cover (Fig. 61). Four to six girdle bands can be found per frustule. The girdle bands are open, tweezer-shaped, and become expanded along the valve to form an enclosed cylindrical-shaped canal (Figs. 62–65). One or two rows of unoccluded areolae align the pars exterior of the girdle band (Figs. 63 and 64). The internal surface, on the side of the canal aligning the cell membrane, consists of a single row of narrow and elongated areolae each with a hymen covering (Fig. 65). Valves range in size from 45–83 µm long, 10–18 mm wide, and have a striae density of 28–30/10 µm.

Original Images

Cite This Page:
Graeff, C. (2012). Frustulia inculta. In Diatoms of the United States. Retrieved April 22, 2018, from

Species: Frustulia inculta

Contributor: Carrie Graeff

Reviewer: Sarah Spaulding


Lange-Bertalot, H. (2001). Navicula sensu stricto, 10 genera separated from Navicula sensu lato, Frustulia. Diatoms of Europe 2: 1-526.

Siver, P.A, Hamilton, P.B. and Pelczar, J. (2009). New species of freshwater diatoms from acidic localities along the Atlantic Coastal Plain of the United States. Botany 87: 409-427. doi:10.1139/B09-015

Links & ID's

Index Nominum Algarum (INA)

Original INA

California Academy of Sciences (CAS)

Frustulia inculta CAS

North American Diatom Ecological Database (NADED)


Autecology Discussion