Frustulia inculta

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.

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