Frustulia cf. krammeri

Graeff, Carrie, Kociolek, John Patrick & Burliga, Ana Luiza, 2012, Valve morphology of four species of Frustulia (Bacillariophyta), including two described as new, Phytotaxa 42, pp. 62-76 : 64-66

Frustulia cf. krammeri ( Figs 1–12 )

Valves linear-lanceolate-rhomboid with rounded, rostrate apices ( Figs 1–6 ), 50.0–62.0 µm in length, 12.0– 14.0 µm in breadth. Striae comprised of round or slightly ovoid areolae, moderately longitudinally organized. Striae parallel only at valve centre; the majority of striae are convergent ( Figs 1 and 2 ). Striae do not completely circumradiate the apices; no areolae present directly between the end of the helictoglossae and the end of the valve ( Figs 3–5 and 7 ). Density of striae 29–30/ 10 µm, consistent across the length of the valve. Areolae at central area and apices relatively small and round ( Fig. 19 ). Internally, areolae occluded by oval or sometimes round coverings ( Fig. 22 ). Longitudinal ribs complete and robust ( Fig. 9 ); ribs thicken significantly before constricting at valve centre to form a figure-8 shape ( Fig. 11 ). Internal porte-crayon structures present, where longitudinal ribs and helictoglossae fuse at valve apices ( Fig. 10 ). Externally, raphe ends form shallow T-shapes ( Figs 7 and 8 ). Often, T-shape not obvious under LM, resulting in raphe ends appearing straight or slightly dilated ( Figs 1 and 5 ). Raphe branches noticeably arched along their length ( Figs. 2 and 4 ). Valvocopulum possesses a notch at mid-valve revealing a row of poroids, visible in slit that runs the perimeter of the valvocopulum, and a field of small irregularly sized and spaced nodules ( Fig. 12 ). In addition to the row of poroids present in the slit, a second row of elongated poroids ornaments the surface of the valvocopula ( Fig. 12 ).

Distribution:— Frustulia cf. krammeri is present in freshwater streams on at least two islands of Hawaii, U.S. A, including Molokai and Kauai.

Observations:— Frustulia krammeri Lange-Bert. & Metzeltin (in Metzeltin & Lange-Bertalot 1998: 96), also known as F. rhomboides (Ehrenb. 1843: 419) Pfitzer (1871: 164) (Lange-Bert. & Jahn, 2000), and F. cf krammeri have similar valve shape, morphology of the striae, and external raphe ends and branches. Our Hawaiian populations of F. cf. krammeri are generally much smaller than F. krammeri , which has a length range of 96–135 µm according to Lange-Bertalot (2001: 169). In addition, the apices of our specimens are more protracted than the relatively large specimens of F. krammeri ( Lange-Bertalot 2001: pl. 128). According to general rules relating size and shape of pennate diatoms (Geitler 1932), if F. cf. krammeri specimens were smaller cells of F. krammeri , we would expect the apices to be more rounded, not more protracted, as is the case in the Hawaiian taxon. Finally, the striae density we measured for F. cf. krammeri (29–30/ 10 µm) is greater than the density of 26–27/ 10 µ m given for F. krammeri ( Lange-Bertalot 2001: 169) . Both morphotypes have a narrow range of striae densities. The description of F. krammeri provided by Lange- Bertalot (2001: 169) states that the species has “poles proper that are free of striae”; this feature is also present in F. cf. krammeri . Frustulia lacrima sp. nov., discussed below, and F. pseudomagaliesmontana Camburn & Charles (2000: 23 ; Metzeltin & Lange-Bertalot 2007: pls. 131 and 132), are two additional species that have striae that do not circumradiate the poles, but those species are otherwise morphologically distinct from F. krammeri and F. cf. krammeri .

Frustulia krammeri has been reported many times well outside its type location of Finland, such as in North Carolina, U.S.A. ( Siver & Hamilton 2011) and Florida, U.S.A. ( Siver & Baskette 2004). However, light and scanning electron micrographs in the same publications above reveal that the morphology of the specimens in our report differ significantly, especially in the appearance of the external central area and apex, the porte-crayon, and the degree of curvature to the longitudinal ribs and raphe system.

Unfortunately, Lange-Bertalot’s (2001) examination of the type material of F. krammeri did not include SEM’s, which may reveal morphological features that more strongly distinguish F. cf. krammeri from F. krammeri .

Figures

FIGURES 1–5. LM. F. cf. krammeri. Valve views showing the size diminution series for specimens from Molokai, Hawaii, U.S.A. Figure 5 is the holotype. Scale bar: 10 µm.

FIGURES 6–12. SEM. F. cf. krammeri. Figs 6–11. External and internal valve views of four specimens. Fig. 6, Full external valve view showing the strongly linear-lanceolate-rhomboid valve shape. Fig. 7, View of external valve apex with striae that do not circumradiate the apices. Fig. 8, External view showing T-shaped raphe endings. Fig. 9, Full internal valve view showing robust longitudinal ribs. Fig. 10, Weak porte-crayon structure and striae that do not circumradiate the poles. Fig. 11, Internal central area showing contricted longitudinal ribs. Fig. 12. View of the valvocopulum showing the notch exposing a random arrangement of tiny nodules. Scale bars: Figs 6, 9: 10 µm; Figs 7– 8, 10 –12: 1 µm.

FIGURES 13–21. LM. F. lacrima. Valve views showing the size diminution series for specimens from Brasil. Figure 19 is the holotype. Note the large degree of variation in valve shape among specimens. Scale bar: 10 µm.

FIGURES 22–27. SEM. F. lacrima. External and internal valve views of five specimens. Fig. 22, Full external valve view of a linear-lanceolate specimen. Fig. 23, External central area showing missing areolae. Fig 24, External view of apices with expanded areolae and striae that do not circumradiate the apices. Fig. 25, Full internal valve view showing the fine valve and delicate longitudinal rib system. Fig. 26, Internal central area with narrow longitudinal ribs and small central nodule. Fig 26A, view of weakly-expressed rectangular internal areolae hymen coverings. Fig 27, Valve apex with minimal longitudinal rib-helictoglossa association and striae that do not circumradiate the apices. Scale bars: Figs 22, 25: 5 µm; Figs 23–24, 26–27: 1 µm; Fig 26A: 0.5 µm.