Humidophila caribaea M. Rybak, Christenh. & Byng 2024, sp. nov.

Humidophila caribaea M.Rybak, Christenh. & Byng, sp. nov. (Figs 1–61) LM observations (Figs 1–33):— Valves linear, slightly gibbous in the valve middle. Valve apices broadly rounded, slightly broader at the valve middle. Valve dimensions (n=40): length 9.0–19.0 µm, width 2.6–3.4 µm. Axial area narrow, linear. Central area rectangular and narrow, reduced in small specimens. Raphe straight and filiform. Proximal and distal raphe endings straight. Striae parallel, hardly discerned in LM, 34–36 in 10 µm. SEM observations (Figs 34–61):— Externally striae composed of single, transapically elongated areola (Figs 34–43). Areolae size uniform along their entire length (Figs 34–43). A break in areole present in the central area (Figs 34–43). In some specimens short, rounded areolae, distinct in their shape and position from other areolae, occasionally present in the central area. Areolae on valve face always present with irregular silica warts in their lumen (Figs 44– 46). Valve face and mantle areolae separated by large hyaline area (Figs 42, 47). Mantle areolae elongated, slit like, becoming smaller and rounded near the apices. Silica warts in mantle areolae absent.An interruption in areolae at valve apices clearly present (Figs 44, 45). External raphe branches straight. Both proximal and distal raphe endings variable even in a single valve, small elongated depressions occasionally present at the endings. Internally, raphe branches straight, proximal raphe endings straight, distal raphe endings terminating on weakly developed helictoglossae (Figs 48–51). Internally areolae covered by hymens. Girdle bands open (Fig. 47, 58–60). Pores on girdle bands present as single row, along valve margins pores strongly elongated with thickened edges (Figs 58–60), becoming smaller and rounded at the apices (Figs 60, 61). No signs of a Voigt discontinuity both in the external and internal view. Type:— GUADELOUPE, the upper slope of Morne Cadet, Trace de Vent Soufflé, Monts Caraïbes, coordinates: 15°58’20.1”N 61°41’24.7”W, ca 680 m a.s.l, coll. date. 3 June 2021, leg: M. Christenhusz & J. Byng, s.n. Holotype slide no. PC0677386 and unmounted material with the same number at the Muséum National d’Histoire Naturelle, Paris, France. Isotype 1 no. SZCZ 28977! and unmounted material with the same number at the Szczecin Diatom Collection (University of Szczecin, Poland). Isotype 2 no. slide no. 2021/29 and unmounted material with the same number at the University of Rzeszów, Poland. The holotype population is presented in figs 1–51. Etymology:— The species epithet refers to the type locality of the new species. Distribution:— So far the species is only known from the type locality. Ecology and associated diatom flora:— The sample was collected from tropical, mesophytic forests on volcanic, pozzolan soil. It was found among terrestrial mosses, sampled during a general botanical expedition to these hills. The species was observed in the sample with acidic pH (6.4) and very low conductivity (60 µS/cm). The most common co-occurred taxa included: Angusticopula cf. dickei (Thwaites) Houk, Klee & H.Tanaka (2017: 25), Chamaepinnularia abdita Metzeltin & Lange-Bertalot (2007: 62), Cosmioneis pusilla (W.Smith) D.G.Mann & A.J.Stickle in Round et al. (1990: 526), three unidentified Eunotia species, Ferocia houkiana Goeyers & Van de Vijver (2020: 9), Humidophila arcuatoides (Lange-Bertalot) Lowe & et al. (2014: 357), H. contenta (Grunow) Lowe & al. (2014: 357), Luticola muticoides (Hustedt) D.G.Mann in Round et al. (1990: 671), L. tomesii Moser, Lange-Bertalot & Metzeltin (1998: 198), Melosira cf. astridae Metzeltin & Lange-Bertalot (2007: 159).