Staurosirella coutelasiana Van de Vijver, 2022

Vijver, Bart Van De, 2022, Two new Staurosirella species (Staurosiraceae, Bacillariophyta) observed in an historic Rabenhorst sample, Phytotaxa 545 (2), pp. 163-174 : 165

publication ID 10.11646/phytotaxa.545.2.5


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Staurosirella coutelasiana Van de Vijver

sp. nov.

Staurosirella coutelasiana Van de Vijver sp. nov. (LM Figs 1–30 View FIGURES 1–68 , SEM Figs 69–73 View FIGURES 69–73 )

Description:— LM ( Figs 1–29 View FIGURES 1–68 (30?)): Frustules in girdle view rectangular, solitary ( Fig. 1 View FIGURES 1–68 ). Colonies not observed. Valves isopolar to occasionally very slightly heteropolar (e.g. Figs 16, 28 View FIGURES 1–68 ), linear-lanceolate in larger specimens to lanceolate, occasionally elliptic-lanceolate in smaller valves. Valve outline in larger specimens often more irregular in shape ( Figs 4, 5 & 8 View FIGURES 1–68 ). Apices broadly rounded, not protracted. Valve dimensions (n=50): valve length 15–35 µm, width 5.0–5.5 µm. Sternum narrow, linear to slightly lanceolate. Striae alternating at both sides of the sternum, parallel to weakly radiate near the valve middle, becoming distinctly more radiate towards the apices, 9–11 in 10 µm. Areolae not discernible in LM.

SEM ( Figs 69–73 View FIGURES 69–73 ): External valve face undulating with raised virgae and striae slightly sunken in ‘punch holelike’ depressions ( Figs 69, 70 View FIGURES 69–73 ). Striae extending without interruption from the valve face onto the mantle gradually narrowing at both ends ( Fig. 71 View FIGURES 69–73 ) giving the striae a lanceolate appearance. Large hyaline zone present at the abvalvar mantle edge ( Fig. 73 View FIGURES 69–73 ). Striae uniseriate, composed of long, slit-like, linear areolae, running parallel to the apical axis ( Figs 69–71 View FIGURES 69–73 ). Vimines not raised. Marginal spines located on the virgae, irregularly shaped (acute to spatulate), originating from one ( Fig. 70 View FIGURES 69–73 ) or two points ( Figs 69, 71 View FIGURES 69–73 ). Spine base hollow ( Fig. 71 View FIGURES 69–73 ). Apical pore fields present at both apices, usually similar in size and shape ( Figs 69–70 View FIGURES 69–73 ), located at the valve face/mantle junction, extending more onto the valve mantle, isolated from neighboring striae. Pore fields composed of small, rimmed pores, arranged in several irregular rows.

Valvocopula with short but well developed fimbriae ( Fig. 72 View FIGURES 69–73 ). Internally, striae distinctly sunken between the flat, doubly flared virgae and sternum ( Fig. 73 View FIGURES 69–73 ). Areolae occluded by irregularly shaped volae, extending from the longer inner side of each vimen ( Fig. 73 View FIGURES 69–73 ).

Type:— SWITZERLAND, Casaccio, south side of the Lukmanier (border between the cantons of Graubünden and Ticino), prepared from Rabenhorst exsiccata sample 1441 (exsiccata set Algen Sachen’s & Europa’s) (holotype BR-4711 !, isotype Slide 402 ( University of Antwerp , Belgium )) . The holotype is represented here by Fig. 11 View FIGURES 1–68 . Duplicates of the Rabenhorst material No. 1441 and Wartmann & Schenk as sample 233 can be found in numerous herbaria worldwide (e.g. Stafleu & Cowan 1983: 465; 1988: 93).

Etymology:— The new species is named after my dear friend, Mrs. Marine Coutelas (Chavignon, France), a young enthusiast French artist with a passion for the world of plants and diatoms.

Comments:— Due to confusion with S. neopinnata , also present in the sample, it is difficult to establish what the smallest specimens of this new species could be. Figure 30 View FIGURES 1–68 represents a short, elliptical valve (length 7 µm) that can represent either S. coutelasiana but also S. neopinnata (see Figs 53–68 View FIGURES 1–68 for the S. neopinnata population observed in the sample). It is impossible to attribute this valve with 100 % certainty to any of both species. Therefore, the smallest valve that undoubtedly can be identified as S. coutelasiana is Fig. 29 View FIGURES 1–68 with a valve length of 15 µm.

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