Staurosirella marginostriata Van de Vijver & V. Peeters sp. nov.

Fig. 1

Holotype.

BR- 4840 (Meise Botanic Garden, Belgium). Fig. 1 C represents the holotype .

Isotype.

Slide 442 (University of Antwerp, Belgium).

Registration.

http://phycobank.org/104533.

Type locality.

Bosbeek (Maaseik, Province of Limburg, Belgium), sample APM 21-91, 51 ° 5.6348 ' N, 5 ° 45.894 ' E, coll. date 25 Jun. 2021, leg. Vlaamse Milieu maatschappij (VMM) .

Description.

LM (Fig. 1 A – R). Frustules in girdle view rectangular, singular. Chains linking several cells in colonies so far not observed. Valves isopolar, strictly lanceolate with convex margins and weakly protracted, rostrate apices. Smaller valves more rhombic-lanceolate with cuneate apices (Fig. 1 R). Valve dimensions (n = 20): length 10–20 µm, width 3.0–4.5 µm. Sternum broad, lanceolate, ghost striae present. Striae short, marginal, 14–15 in 10 µm. Areolae not discernible in LM. SEM (Fig. 1 S – X). Valve face surface undulating with distinctly raised virgae extending almost up to the valve middle (Fig. 1 T), occasionally almost flat (Fig. 1 V). Virgae much broader that the striae. Striae very short, marginal, extending without interruption from the valve face onto the mantle (Fig. 1 S – U, W). Large hyaline zone present at the abvalvar mantle edge (Fig. 1 S – U), terminating at mantle edge by series of irregularly shaped mantle plaques (Fig. 1 S – U). Striae uniseriate, composed of short, slit-like, linear areolae, running parallel to the apical axis (Fig. 1 S – W). Vimines narrow, not raised. Marginal spines located on the virgae, irregular in number (1–3), shape and size (Fig. 1 S – W). Large apical pore fields present at both apices, usually similar in size and shape (Fig. 1 S, T, V), located at the valve face / mantle junction, extending more onto the valve mantle, isolated from neighboring striae. Pore fields composed of usually 4–5 rows of small, rimmed pores (Fig. 1 W). Girdle composed of several probably open, plain copulae (Fig. 1 S – U). Internally, striae distinctly sunken between the raised virgae and the sternum (Fig. 1 X).

Etymology.

The specific epithet marginostriata refers to the short, marginal striae.

Distribution.

At present, only observed in Flanders (type locality) and the Morvan region in France. Confusion with the in LM similarly looking Pseudostaurosira brevistriata (Grunow) D. M. Williams & Round), may be at the base of the unclear distribution.

Ecology and associated diatom flora.

The type locality has an almost circumneutral pH (6.9–7.3), moderate conductivity (160–200 µS / cm), higher nitrate levels (1.4–3.3 mg / l) and sulphate levels (12–30 mg / l). The sample is dominated by Staurosirella stoksiana Van de Vijver sp. nov. (15 % of all counted valves), Aulacoseira ambigua (Grunow) Simonsen (12.5 %), Pseudostaurosira brevistriata (9.5 %), A. granulata (Grunow) Simonsen (9 %), Navicula cryptocephala Kützing (5 %), and N. lanceolata (C. Agardh) Ehrenberg (4 %), pointing to more meso-eutrophic, alkaline conditions (Lange-Bertalot et al. 2017).