Gomphonema vancampianum Van de Vijver, Pottiez & Chavaux, 2024

Van de Vijver, Bart, Pottiez, Margaux & Chavaux, Rémy, 2024, Gomphonema vancampianum sp. nov. (Gomphonemataceae, Bacillariophyceae), a new large Gomphonema species from Europe, PhytoKeys 244, pp. 1-13 : 1-13

Gomphonema vancampianum Van de Vijver, Pottiez & Chavaux sp. nov.

Figs 1 , 2 , 3

Type materials.

Holotype. BR- 4839 (Meise Botanic Garden, Belgium). Fig. 1 C represents the holotype . Isotype. Slide 441 (University of Antwerp, Belgium) .

Registration.

http://phycobank.org/104517.

Type locality.

Lac du Drapeau (Lyon, Département du Rhône, France), sample Drapeau-U 03 - VEG, (coll. date 22. viii. 2023, leg. R. Chavaux).

Etymology.

This species is named in honour of Prof. Dr Karel Van Camp, former Physics professor of the first author at Antwerp University ( Belgium) and life-long enthusiastic amateur diatomist and microscopist.

Description.

LM (Fig. 1 ). Frustules in girdle view narrowly clavate with transapical striae continuing on to the valve mantle without interruption; adjacent to the striae, a line of isolated areolae (Fig. 1 A , arrow). Headpole much broader than the footpole. Valves apiculate-clavate with elliptic-lanceolate upper valve part and largest width right above the valve middle. Lower valve part abruptly narrowing near the valve centre, then gradually tapering towards the acute footpole. Headpole acutely rounded with a narrow protracted, cuneate apex. Occasionally, valves surrounded by marginal crest, visible by changing focal depth (Fig. 1 C, L, N , arrows). Valve dimensions (n = 25): length 30–60 µm, width 10–12 µm. Axial area moderately broad, linear with distinct, shallow markings, visible by changing focal depth. Central area asymmetrical: primary side with more distantly spaced single long stria and stigmoid, well separated near the valve middle. Isolated stria on the secondary side markedly shortened. Raphe clearly lateral and weakly undulating. Central raphe endings indistinct, almost straight. Terminal raphe fissures not discernible in LM. Striae parallel in the middle, soon becoming radiate towards the headpole, but remaining almost parallel or slightly radiate towards the footpole, 10–11 in 10 µm, more closely spaced near the apices. Striae distinctly punctate, 18–24 areolae in 10 µm. SEM (Figs 2 , 3 ). Two types of valves present: with marginal crest (Fig. 2 A – C ) and lacking marginal crest (Fig. 2 D, F ). Valve face and mantle striae in crested valves interrupted at the valve face / mantle junction by the thickened marginal crest. Marginal crest with undulating border near the headpole (Fig. 2 A ). Mantle striae in advalvar part composed of large, densely packed, c-shaped areolae, externally covered by small reniform siliceous flaps. Areolae in abvalvar part of the striae towards the mantle edge, smaller, c- to e-shaped (Fig. 2 A ). Girdle bands broad with continuous row of transapically elongated narrow pores. Marginal crest lowering towards the apices (Fig. 2 B, C ). Valves lacking crest with striae extending almost continuously across the valve face / mantle junction (Fig. 2 F ). Axial area covered with dense irregular pattern of shallow, pit-like depressions (Fig. 2 B, D, E ). Raphe branches clearly undulating (Fig. 2 C, D ). Central raphe endings almost straight, small drop-like (Fig. 2 E ). Distal raphe fissure at footpole bisecting apical pore field, continuing on to the mantle (Fig. 2 F ), at headpole splitting the marginal crest (when present) and continuing shortly on to the mantle (Fig. 2 C ). Apical pore field bisected, composed of several rows of densely packed, rounded pores (Fig. 2 F ), only present at footpole. Striae composed of c-shaped areolae, occluded by small reniform siliceous flaps, near the central area slightly sunken into valve surface (Fig. 2 E ), towards the apices on the same level as the virgae (Fig. 2 F ). Stigmoid external opening small, rounded, sunken into valve face (Fig. 2 E ). Internally valve face surface smooth (Fig. 3 A ). Small pseudoseptum visible at footpole (Fig. 3 A, D ). Striae located in shallow, narrow foraminal rows. Side walls of the areolae with continuous apical bars or small interrupted struts (Fig. 3 C , arrows). Internal opening of the stigmoid short, transversely elongated, located in a long, shallow groove (Fig. 3 B ). Central raphe endings long, right-angled, hook-shaped (Fig. 3 B ). Terminal raphe endings terminating on to well-developed helictoglossae (Fig. 3 D ).

Distribution and ecology.

Gomphonema vancampianum has so far only been found in several samples from the type locality in France. The largest population was found in a sample collected from submerged aquatic plants. The diatom flora is dominated by species typically found in calcium-carbonate rich, oligotrophic lakes with low nutrient concentrations and low saprobity. The sample is dominated by several cymbelloid taxa (e. g. Encyonopsis subminuta Krammer & E. Reichardt , Cymbella affiniformis Krammer , C. lange-bertalotii Krammer , Cymbopleura amphicephala (Nägeli) Krammer ) together with a, so far, unidentified, long-celled Fragilaria species, Brachysira neoexilis Lange-Bertalot , B. cf. chiaruccii Cantonati et al. and Nitzschia cf. subacicularis Hustedt , all indicating the environmental conditions mentioned above ( Lange-Bertalot et al. 2017). The species has also been found in several other French lakes, such as Lac du Réaltor (Provence, France) (Fig. 3 E ) by Luc Ector and Carlos E. Wetzel ( LIST Luxemburg) who, despite an exhaustive review of existing Gomphonema literature, could not assign a name to this species (Wetzel, pers. comm.). It is likely that the species is more abundant than currently known due to confusion with similar taxa, such as G. jadwigiae Lange-Bertalot & E. Reichardt and G. turris Ehrenberg (see Discussion below).

Figures

Figure 1. Gomphonema vancampianum sp. nov. LM micrographs taken from the holotype material (BR- 4839, Lac du Drapeau, Sample DRAPEAU-U 03 VEG, France) A LM picture of a frustule in girdle view. The arrow indicates the smaller, more distantly spaced areolae on the mantle B – O LM pictures of valves in valve face view in decreasing length. The arrows indicate the possible presence of the marginal crest. Scale bar: 10 µm.

Figure 2. Gomphonema vancampianum sp. nov. SEM micrographs taken from the holotype material (BR- 4839, Lac du Drapeau, Sample DRAPEAU-U 03 VEG, France) A SEM external view of the headpole in girdle view showing the marginal crest on both valves, the larger, reniformly occluded upper areolae and the smaller, more distant areolae towards the mantle edge. Note also the slit-like pores on the girdle band B SEM external detail of the upper valve part of a valve bearing a crest showing the lowering marginal crest at the apex C SEM external view of an entire crest-bearing valve. Note the shallow depressions in the axial area D SEM external view of valve without marginal crest. Note the shallow depressions in the axial area and the valve face striae continuing over the valve face / mantle junction E SEM external detail of the central area with the depressed large areolae and the stigmoid. The shallow pit-like depressions are well visible in the axial area F SEM external detail of the footpole with the distal raphe fissure bisecting the apical pore field. Scale bars: 10 µm (A – D), 5 µm (E – F).

Figure 3. Gomphonema vancampianum sp. nov. SEM micrographs taken from the holotype material (BR- 4839, Lac du Drapeau, Sample DRAPEAU-U 03 VEG, France) A SEM internal view of an entire valve B SEM internal detail of the central area with the stigmoid located in a long depression, the hooked central raphe endings and the long foramina with the areolae C SEM internal detail of the areolae with the small silica struts D SEM internal detail of the footpole with the small pseudoseptum, the helictoglossa and the apical pore field E SEM external view of an entire valve with marginal crest from Lac du Réaltor, Provence, France (photo courtesy of Dr Carlos E. Wetzel). Scale bars: 10 µm (A, E), 1 µm (B – D).