Gomphosphenia plenkoviciae Gligora Udovič & Žutinić sp. nov. (Figs 2–42)

Type: CROATIA: Crveno jezero (Red Lake), East side coast, sediment at 20 m depth, collection date: 05.05.2017; leg. B. Jalžić, G. Polić & R. Ozimec; coordinates 38.959390N 095.265483W (Accession No. MKNDC 0011245). Slide MKNDC 0011245/A (holotype) . Slide BRM Zu 10/97 (isotype) .

Frustules in girdle view wedge-shaped (Figs 38, 57, 58). Valves are narrowly clavate to linear and slightly heteropolar in larger specimens to clavate in smaller specimens (Figs 2–36, 43–56). Longer specimens have undulated valve margin and an inflated central part, smaller valves are with convex margins. Headpole rounded, non-protracted, slightly narrower than mid-valve, footpole acutely rounded. Widest part in larger specimens is near the mid-valve, smaller specimens are widest in the upper valve half. Valves are 12–45 μm long and 3.0–6.5 μm wide. Axial area in larger specimens is rather wide, lanceolate, widening towards central area (Figs 2–36); in smaller specimens rather narrow, slightly widened near the central area (Figs 43–56). Central area wide, clearly separated from axial area. Raphe is clearly visible, straight with small, indistinct proximal endings (Figs 37, 39, 40, 60). Internally, the proximal raphe endings are T-shaped (Figs 41, 42, 62). Distal raphe endings externally are very short, straight, slightly expanded into drop-like pores (Figs 37, 39, 40) and not passing on the valve mantle, while internally terminating with distinct helictoglossae (Figs 41, 42, 61). Transapical striae weakly radiate, becoming almost parallel towards poles, 19–22 striae in 10 μm. Striae terminate at the edge of the valve face, and do not extend onto the mantle (Figs 37, 39, 40, 59). Each stria is composed of a single areola. Externally, areolae in the mid-valve have round shape, while towards poles become slightly elongated slits. Internally, areolae appear longer than externally and are covered by fine hymenate occlusions (Figs 40, 61, 62). Two types of striae on the valve mantle were observed. In some specimens (Fig. 57) striae are composed of few (2–4) round areolae, while in other specimens mantle striae are composed of a single areola with slit-like opening (Figs 38, 58, 59). Girdle composed of several open bands (Fig. 38, 57, 58), each bearing a single row of round pores. At footpole, septa, pseudosepta and apical pore field are absent.

Etymology: This species is named in honour of Prof. Anđelka Plenković- Moraj, leading professor in freshwater ecology and phycology at the Department of Biology, Faculty of Science, University of Zagreb.

Distribution: Gomphosphenia plenkoviciae is so far known from Crveno jezero and Krka River. Both localities represent typical karstic environments with high content of CaCO 3 and high conductivity.