Staurosirella stoksiana 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 stoksiana Van de Vijver sp. nov.

Figs 3 , 4

Holotype.

BR- 4842 (Meise Botanic Garden, Belgium). Fig. 3 H represents the holotype .

Isotype.

Slide 444 (University of Antwerp, Belgium) .

Registration.

http://phycobank.org/104535.

Type locality.

Voorste Nete ( Dessel, Province of Antwerp, Belgium), sample 81 a, 51 ° 13.9482 ' N, 5 ° 7.4497 ' E, coll. date 06 Jul. 1994, leg. B. Van de Vijver .

Additional investigated population.

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 (Figs 3 A – AD, 4 A – P). Frustules rectangular, solitary. Chain-like colonies so far not observed. Valves weakly heteropolar, lanceolate to elliptic-lanceolate with convex margins, gradually narrowing towards the non-protracted, broadly rounded apices. Larger valves occasionally slightly ovoid (Fig. 3 C ) in outline with smallest valves almost elliptical (Fig. 3 AD). Valve dimensions (n = 40): length 6–21 µm, width 4.5–5.5 µm. Sternum narrow, linear. Striae alternating, almost parallel becoming very slightly radiate towards the apices, long, almost reaching the sternum, 8–9 in 10 µm. Areolae not discernible in LM. SEM (Figs 3 AE – AK, 4 Q – V). External valve face undulating with slightly raised, flattened virgae and striae sunken in ‘ punch hole-like’ depressions (Figs 3 AE, 4 Q). Striae extending without interruption from valve face onto the mantle, gradually but distinctly narrowing at both ends (Figs 3 AE, AI, 4 S) giving the striae a lanceolate appearance. Abvalvar mantle edge forming a broad hyaline zone, almost half the entire mantle width (Figs 3 AE, 4 Q). Mantle plaques absent. Striae uniseriate, composed of long, slit-like, linear areolae, running parallel to the apical axis (Figs 3 AE, AG, AJ, AK, 4 R, S, U, V). Vimines very thin, not raised. Marginal spines usually present, one to two, located on the virgae, rudimentary, irregularly shaped (blunt, thick, papilla-like). Occasionally mixed populations with spineless and spine valves observed (Fig. 4 R, S, U, V ). Apical pore fields present at both apices. At the footpole, pore field rather large, composed of at least 7 long rows of very small, rounded pores, covering the entire foot pole (Figs 3 AG, 4 U – V). Pore field at the headpole smaller, located on the weakly depressed headpole (Fig. 3 AG, AJ, AK). Valvocopula broad, with short but well developed fimbriae (Fig. 3 AF). Internally, striae distinctly sunken between the flat, doubly flared virgae and sternum (Figs 3 AH, 4 T). Areolae occluded by irregularly shaped volae, extending from the longer inner side of each vimen (Fig. 3 AH).

Etymology.

The new species honours Prof. dr Robby Stoks (Catholic University of Leuven) study friend of the first author, in recognition of his important contributions to the Odonata research.

Distribution.

Staurosirella stoksiana has been regularly observed in samples from Flanders ( Belgium) and the United Kingdom. Most likely the new species has a broader distribution area but due to confusion with the presumably widespread Staurosirella (neo) pinnata and other similar species such as Staurosirella ovata and S. coutelasiana , its exact distribution is not clear. Peeters and Ector (2017, p. 262–263) illustrated several populations from Burgundy (eastern France) under the name Staurosirella ovata , that shows a very large similarity to S. stoksiana .

Ecology and associated diatom flora.

The type population of S. stoksiana was observed in a small lowland river in the Netebekken (Flanders, Belgium). The sample was dominated, apart from S. stoksiana (16 % of all counted valves) by Nitzschia adamata Hustedt (8.7 %), Geissleria decussis (Østrup) Lange-Bertalot & Metzeltin (6.4 %), Navicula gregaria Donkin (6 %), Craticula molestiformis (Hustedt) Mayama (5.1 %), Melosira varians C. Agardh (3.4 %), Planothidium frequentissimum (Lange-Bertalot) Lange-Bertalot (3.2 %), and Cyclotella meneghiniana Kützing (3.2 %). According to the ecological preferences of the observed diatom flora, this indicates meso- to eutrophic, alkaline conditions with medium conductivities ( Lange-Bertalot et al. 2017).

Figures

Figure 3. Staurosirella stoksiana Van de Vijver, sp. nov., LM and SEM micrographs taken from the holotype material (BR- 4842, Voorste Nete, Dessel, Belgium) A, B LM pictures of a frustule in girdle view C – AD LM pictures of valves in valve face view in decreasing length AE SEM external view of a complete frustule in girdle view showing the girdle structure and the mantle AF Complete view of the valvocopula with the large fimbriae AG SEM external view of a complete valve with focus on the apical pore field and the depressed headpole AH SEM internal view of a complete valve AI SEM external view of a complete valve in girdle view AJ – AK Two SEM externals view of a complete, heteropolar valve. Scale bars: 10 µm.

Figure 4. Staurosirella stoksiana Van de Vijver, sp. nov., LM and SEM micrographs taken from an additional population (BR- 4840, Bosbeek, Maaseik, Belgium) A – P LM pictures of valves in valve face view in decreasing length Q SEM external view of a complete frustule in girdle view showing the girdle structure and the mantle R, S SEM external view of two complete valves with focus on the apical pore field and the depressed headpole. Both valves bear a series of marginal spines T SEM internal view of a complete valve U, V Two SEM externals view of a complete, heteropolar valve lacking marginal spines. Scale bars: 10 µm.