Synedra undosa Grunow, 1867

Lobban, Christopher S., Ashworth, Matt P., Camacho, Terance, Lam, Daryl W. & Theriot, Edward C., 2022, Revision of Ardissoneaceae (Bacillariophyta, Mediophyceae) from Micronesian populations, with descriptions of two new genera, Ardissoneopsis and Grunowago, and new species in Ardissonea, Synedrosphenia and Climacosphenia, PhytoKeys 208, pp. 103-184 : 103

Synedra undosa Grunow, 1867

Fig. 17

Reference.

Grunow 1867, p. 4; Grunow 1877, p. 167, pl. 193, fig. 8a-c.

Description from literature.

Very long, to 850 µm, slender, inflated at the center and poles, undulate in between, striae 19 in 10 µm (20-22 according to De Toni 1892). Synedra undosa has the outline of Toxarium undulatum , but linear striae as in Ardissoneopsis appressata .

Materials examined.

Remnant material of Grunow 839-4611 [W catalog # W0127010, Acquisition # W-1901-0004611]. Not found in Micronesian samples.

Observations.

We have not encountered this in the Guam flora but found several fragments in Grunow’s Honduras gathering that showed internal and external structure, confirming the similarity of structure to the two aforementioned Ardissoneopsis spp. A fragment including the central inflation and one pole suggests a total length of ca. 690 µm (Fig. 17A ). Widths were 10-11 µm across the center, 9 µm across the poles and 4-5 µm between; stria density 19-21 in 10 µm. The annulus along valve face-mantle junction at least partially subtended by longitudinal costae (Fig. 17B-E ). Transverse costae also evident throughout except near poles (Fig. 17F-H ). No pseudoseptum. Valvocopula and copula both with multiple rows of pores in decussate pattern on exterior, one row of interior pores, fimbriate inner margin and lacking sculpted apices (Fig. 17I ). Copula wider, with fimbriae commonly bifurcated.

Taxonomic comments.

According to AlgaeBase (Miranda in Guiry and Guiry 2020), S. undosa is currently referred to as Toxarium undosum (Grunow) De Toni, 1892, which De Toni recognized as distinct from T. undulatum . We have not found more recent mention of this species, but it clearly cannot remain in Toxarium . Hustedt (1931-1959, pp 224-225) stated that, while Grunow had made clear the abundance of Synedra undosa in his Honduras material, "one must assume he also included S. (Toxarium) undulata ," because Hustedt had not observed specimens matching Grunow’s drawings in Honduras material he examined. Hustedt concluded that this species requires further examination. Grunow, however, was clear that S. undosa was different from S. undulata and the SEM images here clearly prove him right. On the evidence that it is a species in its own right, we propose below its transfer to Ardissoneopsis .

Figures

Figure 17. Synedra undosa from Grunow's Honduras material A internal view of half valve, total length would have been ca. 690 µm B external view of fragment of frustule including the central inflation C external view of valve fragment with pole D external view of valve fragment near central area showing the strong undulation E detail of external pole showing annulus (double-headed arrow) and spines F-H internal views of central, near central (cf. D), and polar portions of valve, respectively, showing longitudinal costae (arrows) and transverse costae; transverse costae developing gradually toward left in H. I girdle bands, showing fimbriate valvocopula and copula with glimpses of interior costate surface of valve. Scale bars: 100 µm (A); 15 µm (B, C); 10 µm (D-I).