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

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

Description:— LM ( Figs 1–29 (30?)): Frustules in girdle view rectangular, solitary ( Fig. 1 ). Colonies not observed. Valves isopolar to occasionally very slightly heteropolar (e.g. Figs 16, 28 ), 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 ). 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 ): External valve face undulating with raised virgae and striae slightly sunken in ‘punch holelike’ depressions ( Figs 69, 70 ). Striae extending without interruption from the valve face onto the mantle gradually narrowing at both ends ( Fig. 71 ) giving the striae a lanceolate appearance. Large hyaline zone present at the abvalvar mantle edge ( Fig. 73 ). Striae uniseriate, composed of long, slit-like, linear areolae, running parallel to the apical axis ( Figs 69–71 ). Vimines not raised. Marginal spines located on the virgae, irregularly shaped (acute to spatulate), originating from one ( Fig. 70 ) or two points ( Figs 69, 71 ). Spine base hollow ( Fig. 71 ). Apical pore fields present at both apices, usually similar in size and shape ( Figs 69–70 ), 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 ). Internally, striae distinctly sunken between the flat, doubly flared virgae and sternum ( Fig. 73 ). Areolae occluded by irregularly shaped volae, extending from the longer inner side of each vimen ( Fig. 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 . 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 represents a short, elliptical valve (length 7 µm) that can represent either S. coutelasiana but also S. neopinnata (see Figs 53–68 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 with a valve length of 15 µm.

Figures

FIGURES 1–68. Light micrographs of three Staurosirella species observed in Rabenhorst sample 1441. 1–30. Staurosirella coutelasiana Van de Vijver sp. nov. LM views of the population arranged in decreasing length. Fig. 1. represents a frustule in girdle view. 31–51. Staurosirella minutissima Van de Vijver, sp. nov. LM views of the population arranged in decreasing length. Figs 31 and 32 represent frustules in girdle view, either inpairs (31)or solitary (32). 52 represents a possible valvocopula.52–68.Staurosirella neopinnata E.Morales et al. LM views of the population arranged in decreasing length. 68. Represents two frustules in girdle view. Scale bars = 10 µm.

FIGURES 69–73. Staurosirella coutelasiana Van de Vijver sp. nov. SEM images taken from the holotype material (BR-4711, Rabenhorst sample 1441, Casaccio, Switzerland). 69–71. Three external views of an entire valve. Note the presence of the irregular marginal spines and the rather well-developed apical pore field at each apex. The virgae and sternum are clearly raised with the striae as punch-holes. 72. External view of the open valvocopula showing fimbriae. 73. SEM internal view of an entire valve. Scale bars = 10 µm.