Frustulia lacrima Graeff, Kociolek

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 : 66-68

Frustulia lacrima Graeff, Kociolek , et Burliga, sp. nov. ( Figs 13–27 ; Figure 19 = holotype)

Valvae maxime tenues, lineares-lanceolatae apicibus anguste rotundatibus protractibus moderate, aliqui lineares ultra ceterae. Longitudo 33.5–53.5 µm. Latitudo 8.0– 10.5 µm. Striae 37–38/ 10 µm, parallelae ad centro, convergentes versus apices. Striae convergentesrectae, sed saepe undulatae. Areolae generatim ovales, sed ubi contiguae helictoglossae, interne et externe, expansae lineares ovales ad lacriformes. Areolae interdum absens propeaream centralam. Areolae aliquot ad extrema, nullae inter helictoglossam et apicem.

Type: — BRASIL. Carajás National Forest in Pará. (Holotype ANSP GC26817 , Fig. 19 ; Isotype COLO 3344 ) .

Valves extremely fine, linear-lanceolate ( Figs 16–22 ) or occasionally rhomboid in shape ( Figs 15 and 25 ). Some specimens appear with more linear margins than others ( Figs 19 and 21 ). Apices narrowly rounded and moderately rostrate ( Figs 15, 17 , and 19) to strongly rostrate ( Figs 13 and 20 ); 33.5–53.5 µm in length, 8.0– 10.5 µm in breadth. Striae 37–38 in 10 µm, parallel at valve centre, convergent towards poles. Striae nearly straight ( Figs 15 and 20 ) or often wavy, especially near apices ( Figs 16 and 17 ). Few areolae present at apices, striae do not circumradiate poles ( Figs 24 and 27 ). Areolae highly organized in the longitudinal direction ( Figs 17 , 24 and 27 ). Areolae generally ovoid, but those adjacent to helictoglossae, internally and externally, expanded into either a larger oval or teardrop shape ( Figs 17 , 24 and 27 ). Internally, hymenes with weakly rectangular coverings ( Fig. 26A ). A few areolae sometimes absent near central area ( Figs 13 and 23 ); central area extremely narrow ( Figs 18 and 20 ). Longitudinal ribs complete, relatively fine ( Fig. 25 ). Although longitudinal ribs fuse with the helictoglossa at the apices, the connection between the two structures is highly reduced; porte-crayon not present ( Fig. 27 ). Longitudinal ribs fuse with the central nodule and constrict slightly forming a generally narrow structure ( Fig. 26 ). External raphe ends slightly dilated ( Figs 23 and 24 ).

Etymology:— The species epithet is derived from the Latin word meaning “tear,” which describes the tear-drop shaped areolae at the valve apices.

Distribution:— Frustulia lacrima is found in lakes in Carajás National Forest in Pará, Brasil.

Observations:— Frustulia lacrima specimens often exhibit a valve shape that is a departure from the rhomboid shape common found in typical Frustulia taxa, though there are other linear species inhabiting South America and the southern United States such as F. pseudomagaliesmontana ( Camburn & Charles 2000, Siver & Baskette 2004, Metzeltin & Lange-Bertalot 2007: pls. 131 and 132), F. magaliesmontana Cholnoky (1957: 349 ; Metzeltin & Lange-Bertalot 2007: pl. 137) and F. zizkae Lange-Bertalot (in Metzeltin & Lange- Bertalot 1998: 106). Additional morphological similarities between F. lacrima and F. pseudomagaliesmontana exist, such as the slightly expanded external raphe ends, rectangular internal hymen coverings, lack of striae circumradiating the poles, and appearance of the rib-helictoglossa structure, though the helictoglossa in F. lacrima is slightly more linear than that observed in F. pseudomagaliesmontana ( Siver & Hamilton 2011: pl. 147, Siver & Baskette 2004). Frustulia lacrima is also proportionally and absolutely broader than F. pseudomagaliesmontana , which has a length range that overlaps with F.lacrima but recorded breadth ranges of only 6.0– 6.5 µm ( Camburn & Charles 2000) and 4.8–6.5 µm ( Siver & Baskette 2004). In addition, SEM images of F. pseudomagaliesmontana from Florida, U.S.A. ( Siver & Baskette 2004) and North Carolina, U. S. A. ( Siver & Hamilton 2011: pl. 147, fig. 2) illustrate the species lacking the expanded areolae seen at the apices of F. lacrima .

Figures

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.