Staurosirella moralesii Van de Vijver, Jüttner & D. M. Williams, 2024

Van de Vijver, Bart, Kusber, Wolf-Henning, Jüttner, Ingrid, Schuster, Tanja M. & Williams, David M., 2024, Revision of the Staurosirella leptostauron complex (Staurosiraceae, Bacillariophyta) in Europe with the description of three new species, Plant Ecology and Evolution 157 (2), pp. 174-201 : 174-201

Staurosirella moralesii Van de Vijver, Jüttner & D. M. Williams sp. nov.

Figs 5 , 6 , Supplementary material 8

Type locality.

Willow Creek, Waushara, Wisconsin, USA Western Lake Michigan Drainage study Unit, 1993 ( ANSP G. C 100049 b).

Holotype.

ANSP G. C 100049 b ( Academy of Natural Sciences , Philadelphia). Figure 5 F illustrates the holotype.

Registration.

http://phycobank.org/103340

Analysed material.

UNITED STATES • Willow Creek, WI; sample ANSP G. C 100049 b, material kept at The Academy of Natural Sciences, Philadelphia, new slide deposited as BR- 4826; BR, ANSP.

LM description.

Valves almost isopolar, with a slightly larger footpole, rhombic throughout the entire cell diminution series. Larger specimens more elongated than smaller, more compact valves. Apices acutely rounded, not protracted. Valve dimensions (n = 25): length 10–40 µm, width 5–9 µm. Sternum variable, moderately broad, mostly lanceolate, to narrow and linear in some valves (Fig. 5 T ). Striae much broader than the virgae, parallel in the middle, becoming weakly radiate at the apices, 7–8 in 10 µm. Areolae not discernible in LM. Figure 5 .

SEM description.

Valve face irregular with weakly raised virgae bearing parallel very low ridges. Series of large, flattened marginal spines present on the virgae, due to erosion often split into several parts (Fig. 6 B ). In non-eroded valves, granules scattered all over valve mantle and the valve margin, usually located on the vimines (Fig. 6 C ). Striae composed of linear, slit-like areolae, separated by thin vimines. Striae much broader than the virgae. Areolae gradually diminishing in length towards the sternum and the valve face / mantle junction, widening again slightly on the mantle (Fig. 6 A ). Apical pore fields present on both apices. At the footpole, pore field rather large, composed of at least 7 long rows of small, rounded pores, covering the entire foot pole (Fig. 6 C ). Pore field at the headpole smaller, located on the weakly depressed headpole (Fig. 6 A – C ). Internally sternum flat connected to the virgae (Fig. 6 D ). Apical pore fields clearly visible with a distinct difference in size between footpole (larger) and headpole (smaller), indicating the heteropolarity of the valves. Valvocopula with distinct fimbriae, often with dentated edge (although possibly a result of weak valve erosion) (Fig. 6 E – F ). Figure 6 .

Etymology.

The species is named after the late Dr Eduardo A. Morales (University of Evora, Portugal) who suddenly passed away in May 2023. Eduardo was a world-renowned specialist of the taxonomy and morphology of small-celled araphid genera and described many species in the genera Staurosirella .

Associated diatom flora.

The Willow Creek sample is entirely dominated by several species of Staurosirella . Apart from S. moralesii , S. ovata E. Morales & Manoylov and S. manoyloviana had high relative abundances. However, Morales and Manoylov (2006 b) pointed out that the low proportion of S. moralesii (reported as S. rhomboides ) they observed was an indication that they did not have their optimal conditions in this river. In contrast, our observations of the type slide showed a rather high abundance of S. moralesii . According to Morales and Manoylov (2006 b), Willow Creek in Wisconsin has relatively warm (19.5 ° C) and basic (pH 8.2) waters with medium conductivity (348 µS / cm), a nitrate and nitrite concentration of 1.20 mg / L, and an orthophosphate concentration of 0.10 mg / L. Other frequent species in the sample include Amphora indistincta Levkov , Cocconeis pediculus Ehrenb. , C. pseudothumensis , Geissleria acceptata (Hust.) Lange-Bert. & Metzeltin , several species of Gomphonema , Karayevia clevei (Grunow) Bukht. , Navicula tripunctata (O. F. Müll.) Bory , and Psammothidium lauenburgianum (Hust.) Bukht. & Round. Most of these species are characteristic for alkaline waterbodies with higher trophic levels (meso-eutrophic) ( Lange-Bertalot et al. 2017).

Figures

Figure 5. Staurosirella moralesii Van de Vijver, Jüttner & D. M. Williams sp. nov., LM micrographs taken from the type material (ANSP G. C 100049 b, Willow Creek, United States). A – Z. LM pictures of valves in valve face view in decreasing length. Note the change in valve outline in the smaller valves. Scale bar = 10 µm.

Figure 6. Staurosirella moralesii Van de Vijver, Jüttner & D. M. Williams sp. nov., SEM micrographs taken from the type material (ANSP G. C 100049 b, Willow Creek, United States). A – C. SEM external view of three complete valves, showing the variation in the shape and size of the sternum, the differences in shape and size in apical pore field between head- and footpole. D. SEM internal view of a complete valve. E – F. SEM view of the valvocopula with the fimbriate extensions in oblique and frontal view. Scale bar = 10 µm.