Staurosirella vanheurckiana Van de Vijver, Ballings & M. de Haan 2024, sp. nov.
Creators: name: Van de Vijver, Bart
name: Peeters, Valérie
name: Hansen, Iris
name: Ballings, Petra
name: de Haan, Myriam
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Chromista
Ochrophyta
Bacillariophyceae
Fragilariales
Fragilariaceae
Staurosirella
Staurosirella vanheurckiana

description: Staurosirella vanheurckiana Van de Vijver, Ballings & M. de Haan sp. nov.   
Fig. 6  
Holotype.  
BR- 4844 (Meise Botanic Garden, Belgium). Fig. 6 J represents the holotype.  
Isotype.  
Slide 446 (University of Antwerp, Belgium).  
Registration.  
http://phycobank.org/104537.  
Type locality.  
Leuven, Belgium, Van Heurck exsiccata set Types du Synopsis 315, leg. (probably) Père Gautier  
Description.  
 LM (Fig. 6 A – AE). Frustules in girdle view rectangular, solitary or in pairs. Ribbon-like colonies so far not observed. Valves heteropolar, lanceolate to elliptic-lanceolate throughout the entire cell diminution series, with convex margins, gradually narrowing towards the acutely rounded foot pole. Head pole broadly rounded. Smaller specimens ovoid in shape (Fig. 6 S – AE). Valve dimensions (n = 40): length 8–22 µm, width 3.0–3.5 µm. Sternum moderately narrow, lanceolate. Striae alternating, almost parallel to very slightly radiate throughout, 8–10 in 10 µm. Areolae not discernible in LM. SEM (Fig. 6 AF – AL). External valve face almost flat with very slightly raised virgae and striae sunken in ‘ punch hole-like’ depressions (Fig. 6 AI). Abvalvar mantle edge forming a broad hyaline zone, almost half the entire mantle width (Fig. 6 AF). Virgae broader than the striae. Striae extending without interruption from valve face onto the mantle (Fig. 6 AI – AJ), gradually narrowing towards the ends (Fig. 6 AF – AI) giving the striae a lanceolate appearance. Striae uniseriate, composed of long, slit-like, linear areolae, running parallel to the apical axis (Fig. 6 AG – AI). Vimines very thin, not raised. Spines absent. Apical pore fields present, different on both apices. Smallest pore field present at head pole, located on small depression (Fig. 6 AG – AI). At footpole, apical pore field large, composed of a large number of parallel rows of very small rounded pores (Fig. 6 AJ). Internally, striae distinctly sunken between the flat, doubly flared virgae and sternum (Fig. 6 AK – AL). Due to erosion, areola occlusions no longer observed.   
Etymology.  
The new species is named in honour of Henri Van Heurck (1838–1909), the most famous Belgian diatomist whose Types du Synopsis Atlas (Van Heurck 1880–1885) was one of the first comprehensive illustrated diatom monographs in the world.  
Distribution.  
 Staurosirella vanheurckiana has so far only been found in the type locality, most likely due to confusion with similar taxa such as Staurosirella ovata.   
Ecology and associated diatom flora.  
 The type sample is one of the samples in the Van Heurck exsiccata set Types du Synopsis des Diatomées de Belgique (Van Heurck 1882–1885). The sample was labelled “ Fragilaria mutabilis (W. Sm.) Grun. formae minores ” and was collected near Louvain (Leuven, prov. Vlaams Brabant, Belgium). The original vial of the sample also mentions the number “ 291 ” although it is unclear to what number this refers. Van Heurck (1885, p. 157) mentions that the Louvain sample was collected by P. G., which most likely stands for Père Vincent Gautier (1827–1903), who collected a large amount of samples that are now conserved in the Van Heurck collection in BR. The sample is dominated by S. vanheurckiana reaching more than 50 % of all counted valves. Other, subdominant species include Encyonema ventricosum (C. Agardh) Grunow, Melosira varians C. Agardh, Nitzschia linearis (C. Agardh) W. Smith, Ulnaria cf. verhaegeniana Van de Vijver et al., Gomphonema capitatum Ehrenberg, Planothidium lanceolatum (Brébisson) Lange-Bertalot, Amphora ovalis, and Meridion circulare (Gréville) C. Agardh, but they never reached more than 2 % of the total flora. This diatom flora most likely points to medium to higher trophic levels, and organic pollution up to the β-α- mesosaprobic levels (Lange-Bertalot et al. 2017).
description: Published as part of 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, pp. 139-160 in PhytoKeys 242 on pages 139-160, DOI: 10.3897/phytokeys.242.122458