Tryblionella calida Stroganov
Year: 2026
Type: article
Abstract: Tryblionella calida (Grunow) Stroganov Figs 1, 2, 3, 4 Description. LM (Fig. 1). Valves linear-lanceolate with wedge-shaped, slightly protruding apices. Valve dimensions (n = 17): length range 38–61 μm, width range 8.6–10.6 μm at the constricted middle part. Valve surfaces only slightly undulate from side to side, appearing almost flat. Axial sternum absent. Transapical ribs parallel, continuous across valve surface, 15–17 in 10 μm. Raphe system eccentric, located along one side of valve. Fibulae visible, short, rectangular to square (e. g., Fig. 1 E, H, arrows), 9–10 in 10 μm. Ratio of transapical-ribs density to fibula density ca. 1.6. SEM (Figs 2, 3, 4). Transapical ribs elevated, continuously across valve surface (Fig. 2 A, B). Striae uniseriate, 34–36 in 10 μm (measured on SEM images, n = 3). Marginal ridge is a high standing silica lamella, composed of a bottom part with long slit-like fenestrae (labelled in Fig. 2 E, F) and a top part, smooth with a plain margin (Fig. 2). Distal mantle shallow, lacking ornamentations (Figs 2, 4 A, C, D). Central nodule present (Fig. 2 C, D, arrow; Fig. 4 B, arrow), distal raphe fissures curved (Fig. 2 E, F, curved arrows). A longitudinal row of short bar-like ribs is produced along the raphe canal wall from pole to pole (Fig. 2 D – F, double-headed arrows). Row of poroids is produced in the raphe canal wall on the side of valve surface (Fig. 2 E, F, arrows). Inner openings of areolae rounded, rimmed. Proximal mantle very deep so that it often hides the short fibulae (Fig. 3 A). Proximal mantle composed of two parts: advalvar part (composed of bar-like ribs and narrow, rectangular openings, labelled in Fig. 3 D), and abvalvar part (hyaline without ornamentations, labelled in Fig. 3 B). A row of poroids produced in the raphe canal wall on the side of the proximal mantle (Fig. 3 B – D, arrows). Inner central raphe fissure straight, central nodule helictoglossa-like (Fig. 4 B, arrow). Fibulae squat, some apically elongated (Fig. 4 C, D, arrows). Helictoglossae small (Fig. 4 C, D, curved arrows). Comments. The basionym of Tryblionella calida is Nitzschia calida Grunow (in Cleve and Grunow 1880). Grunow’s protologue, written in German, reads: “ N. calida Grunow. Klein, Schaalen linear länglich, meist in der Mitte schwach verengt, mit keilförmigen, schwach vorgezogenen Spitzen. Längsfalte breit, sehr flach, oft kaum sichtbar. Querstreifen 17–19 in 0.01 mm., Kielpunkte klein, rund, circa 10 in 0.01 mm. Länge 0.034–0.043 mm., Schaalenbreite 0.009–0.01 mm. In den Thermen von Ofen in Ungarn. […] ” (Cleve and Grunow 1880, p. 75). The specimens examined fit Grunow’s protologue in valve morphology (e. g., especially the almost flat valve face), overlapping valve sizes (38–61 μm vs. 34–43 μm in length, 8.6–10.6 μm vs. 9–10 μm in width), overlapping density of transapical ribs (15–17 in 10 μm vs. 17–19 in 10 μm), overlapping fibula density (9–10 in 10 μm vs. 10 in 10 μm), and their occurrence in freshwater habitats. Outside Europe, Kociolek (2011) provided observations of T. calida based on specimens collected from America and provided the following description: “ […] A narrow, indistinct fold runs along the longitudinal axis of the valve. The fold is barely undulated or may even appear not to rise or taper from the main valve surface. […]. ” Thus, Kociolek also noted the almost flat valve faces in T. calida. SEM observations of T. calida are available in Metzeltin et al. (2005, plate 109) and Bertolli et al. (2020, Fig. 5 D – G), but these studies provided only low-magnification images and did not show many details of the frustule ultrastructure. In this paper, the ultrastructure of its marginal ridge, proximal and distal mantles, and fibulae is described and illustrated in detail for the first time. Thus, based on the protologue and the observations presented here, the following diagnostic criteria are proposed for T. calida. These include a linear-lanceolate valve outline with wedge-shaped, slightly protruding apices, a very slightly undulate valve surface, elevated transapical ribs continuous across the valve face and short bar-like ribs connecting the raphe canal wall, uniseriate striae, squat and sometimes apically elongated fibulae, and a high marginal ridge composed of a bottom part with elongated slit-like fenestrae and a solid top part with a plain margin. Stroganov (1927) made the valid transfer of Nitzschia calida Grunow (in Cleve and Grunow 1880) to Tryblionella before Mann (in Round et al. 1990). Therefore, the combination Tryblionella calida (Grunow) D. G. Mann should not be used.
Language: English
Topic: Diatoms and Algae Research
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W7204192435