Staurosirella binodiformis Van de Vijver, 2024

Van de Vijver, Bart, Peeters, Valérie, Hansen, Iris, Ballings, Petra & de Haan, Myriam, 2024, Five new species in the genus Staurosirella (Bacillariophyta) from European freshwater habitats, PhytoKeys 242, pp. 139-160 : 139-160

Staurosirella binodiformis Van de Vijver sp. nov.

Fig. 2

Holotype.

BR- 4841 (Meise Botanic Garden, Belgium). Fig. 2 E represents the holotype .

Isotype.

Slide 443 (University of Antwerp, Belgium) .

Registration.

http://phycobank.org/104534.

Type locality.

outflow from a small lake near Þingvellir , Iceland, sample 29, coll. date 15 Jul. 1954, leg. Niels Foged .

Description.

LM (Fig. 2 A – AP). Valves isopolar, linear, slightly constricted near the valve center in longer specimens (Fig. 2 A – G ), becoming linear, linear-lanceolate to even almost elliptical in smallest specimens (Fig. 2 AM – AP). Apices in longer specimens protracted, rostrate to subcapitate, to not protracted, broadly rounded in smaller valves. Valve dimensions (n = 50): length 6–21 µm, width 3.0–3.5 µm. Sternum narrow, linear. Striae almost parallel weakly radiate in the valve center, becoming more radiate towards the apices, long, almost reaching the sternum, 14–15 in 10 µm. Areolae not discernible in LM. SEM (Fig. 2 AQ – AV). Valve face surface weakly undulating with raised virgae extending almost up to the valve middle (Fig. 2 AR – AT). Virgae almost double as broad as the striae. Striae long, extending without interruption from the valve face onto the mantle (Fig. 2 AQ). Very large hyaline zone present at the abvalvar mantle edge (Fig. 2 AQ). Mantle plaques absent (Fig. 2 AQ). Striae uniseriate, composed of slit-like, linear areolae, running parallel to the apical axis (Fig. 2 AQ – AU). Areolae diminishing in size towards the sternum (Fig. 2 AT), becoming almost rounded at the sternum. Mantle striae often very short, reduced to only one areola (Fig. 2 AU), occasionally also longer (Fig. 2 AS). Vimines very narrow, not raised. Irregular but dense series of short, marginal spines located on the virgae, usually bordering immediately the striae (Fig. 2 AR – AS). Spines occasionally bifurcated (Fig. 2 AQ, AS). Apical pore fields present at both apices, usually similar in size and shape (Fig. 2 AR – AT), located at the valve face / mantle junction, extending more onto the valve mantle, isolated from neighbouring striae. Pore fields composed of usually 2–3 rows of small, rimmed pores (Fig. 2 AU). Girdle composed of several open, plain copulae (Fig. 2 AQ). Internally, striae distinctly sunken between the raised virgae and the sternum (Fig. 2 AV).

Etymology.

The specific epithet binodiformis refers to the outline resemblance with Staurosira binodis Ehrenberg.

Distribution.

At present, only observed in Iceland on the type locality, probably due to confusion with Staurosira binodis and Staurosirella oldenburgiana (Hustedt) E. Morales.

Ecology and associated diatom flora.

Niels Foged (1906–1988) collected the sample in 1954 from stones covered with moss and green algae in the outflow from a small lake near Þingvellir on the road between Reykjavik and Þingvellir, north of Mosfellsheidi ( Iceland). The sample is dominated by a large number of small-celled araphid taxa belonging to the genera Staurosira , Staurosirella and Pseudostaurosira D. M. Williams & Round. As most of these taxa most likely belong to currently undescribed species, it is hard to derive the ecology from them. Several raphid taxa were observed, but in much lower frequencies such as Placoneis explanata (Hustedt) Mayama , Planothidium joursacence (Héribaud) Lange-Bertalot , Skabitschewskia peragallii (Brun & Héribaud) Kulikovskiy & Lange-Bertalot , Cavinula jaernefeltii (Hustedt) D. G. Mann & Stickle , and C. pusio (Cleve) Lange-Bertalot. Most likely, the diatom flora points to oligo- to mesotrophic, colder, pioneer conditions ( Lange-Bertalot et al. 2017).

Figures

Figure 2. Staurosirella binodiformis Van de Vijver, sp. nov., LM and SEM micrographs taken from the holotype material (BR- 4841, Foged sample 29) A – AP LM pictures of valves in valve face view in decreasing length AQ SEM external view of a complete valve in girdle view showing the girdle structure and the mantle AR SEM external view of a complete valve. Note the slight constriction at the valve middle, the undulating valve face surface and the series of spines AS SEM external view of a complete valve with focus on the apical pore field and the transition between valve face and mantle AT SEM external view of a complete valve AU SEM external detail of a valve apex showing the large apical pore field AV SEM internal view of a complete valve. Scale bars: 10 µm (A – AS, AV); 1 µm (AU).