Microcostatus labrisicus M.Rybak, Kochman-Kędziora, Luthfi, 2022

Mateusz, Rybak, Natalia, Kochman-Kędziora & Muzaky, Luthfi Oktiyas, 2022, A new diatom (Bacillariophyta) species from Indonesian urban areas, description of Microcostatus labrisicus sp. nov., Phytotaxa 555 (1), pp. 87-94 : 88

Microcostatus labrisicus M.Rybak, Kochman-Kędziora, Luthfi , sp. nov. ( Figs 1–19 )

LM observations ( Fig. 1–13 ): — Valves lanceolate to elliptical-lanceolate with convex valve margins and slightly protracted apices. Valve dimensions (n=25): length 6.0–8.5 µm, width 3.0–3.5 µm, length/width ratio 2.0–2.6. Striae invisible in light microscopy. Raphe branches straight. Proximal raphe and distal raphe endings barely visible. The shape of central area only visible in SEM, visible in LM as labrys-shaped shadow.

SEM observations ( Fig. 14–19 ): — Striae radiate (~ 50 in 10 µm), composed of one row of round to slightly elongated areolae, externally not occluded ( Figs 14, 15 ). Central area large, labrys-shape, bordered by ~10 shortened striae (often with only one areola) positioned on both sides, close to the valve margins. Raphe straight, filiform, located in raised constricted sternum with much reduced conopeum ( Figs 14, 15 ). Conopeum wider near the proximal raphe endings, tapering towards apices. Proximal raphe fissures widely separated lying in spathulate lipped grooves ( Fig. 15 ). Distal raphe fissures hooked and deflected to the same side ( Figs 16, 17 ). Longitudinal depressions, narrowing towards the apices positioned on both sides of sternum, separated by thickened fascia. Small microcostae with irregular silica granules visible in longitudinal depressions. A single row of rounded to slightly elongated pores present on the valve mantle ( Figs 14, 16, 17 ). Internally areolae are clearly separated and not occluded by hymenes, striae separated by slightly thickened virgae. Raphe branches straight with spathulate proximal raphe endings. The central area is broad, bow-tie in shape ( Figs 18, 19 ).

Type:— Borneo Island , Gaharu Park, Sambas, Sambas distric, 1°21’52.7”N 109°18’36.8”E, coll. date 04 August 2017. Holotype- slide no. SZCZ28436 ! and unmounted material with same number at the Szczecin Diatom Collection , University of Szczecin, Poland. Isotype- slide no. 2017/569 and unmounted material with the same number at the University of Rzeszow, Poland. Holotype specimen designated here, Fig. 7 .

Etymology:— The species epithet “labrisicus” refers to the shape of the central area resembling a “ labrys ” – a double-headed axe.

Distribution:— So far only observed from the type locality.

Associated diatom flora:— Placoneis geitleri ( Hustedt1937: 263) Vishnyakov , Eunotia isabelensis LangeBertalot, Bąk & Kociolek ( Bąk et al. 2017: 213), Humidophila contenta (Grunow in Van Heurck 1885: 109) Lowe et al. ( Lowe et al. 2014: 357), Luticola muticoides ( Hustedt 1949: 82) D.G.Mann ( Round et al. 1990: 671), Luticola sp. , Microcostatus stapputana Lange-Bertalot & Wydrzycka (in Wydrzycka & Lange-Bertalot 2001: 12). The associated diatom flora is illustrated at figs 20–38. The diatom assemblages have a low abundance and are species-poor. In the analyzed sample only 7 taxa were observed and all of them occurred rarely.

Figures

FIGURES 1–19. Microcostatus labrisicus sp. nov. Figs 1–13. Light micrographs of the holotype population, fig. 7 represents the holotype specimen. Figs 14–17. Scanning electron microscopic (SEM) images of external view. Fig. 14. External view of the entire valve. Fig. 15. External detail of the central area and central parts of longitudinal depressions. Figs 16–17. External detail of the distal raphe endings and microcostae. Fig. 18. Internal detail of the central area and proximal raphe endings. Fig. 19. Internal valve view. Scale barrepresents 5 µm (Figs 1–13), 4 µm (Fig. 14), 3 µm (Fig. 19), 1 µm (Figs 15–18).