Mayamaea spirans (Hust. ex Simonsen 1987: 175) Lange-Bert. (2001: 141)

Mayamaea spirans (Hust. ex Simonsen 1987: 175) Lange-Bert. (2001: 141)

Lectotype: slide BRM N17 About BRM /57, Sample AT 1 (Ovalau, ‘ Südsee an Algen ’), Fiji.

Description: Valves elliptic with convex to parallel margins and broadly rounded, never protracted apices. Valve dimensions (n=20): length 9–10 μm, width 3.5–4.5 μm. Axial area wide, linear, conforming with the sternum. Central area almost entirely lacking. Raphe straight, enclosed in a heavily silicified sternum. Distal raphe fissures not discernible in LM. Striae strongly radiate throughout the entire valve, 17–20 in 10 μm. Central striae alternatingly shortened. Areolae not discernible in LM ( Figs 2–11 View FIGURE 1–17 ).

SEM observations ( Figs 12–17 View FIGURE 1–17 ): Wide sternum visible and heavily silicified central nodule present. Striae composed of several square to rounded areolae, ca. 50 in 10 μm, covered externally by clearly porous hymenes. Areolae becoming more elongated near the valve mantle ( Figs 16–17 View FIGURE 1–17 ). External raphe branches straight with distinctly enlarged, drop-like, not deflected proximal raphe endings. Distal raphe fissures straight, barely deflected opposite to the proximal raphe endings, never continuing onto the mantle but terminating near the last striae at the apices ( Figs 12–16 View FIGURE 1–17 ). Internal raphe branches straight with simple proximal raphe endings. Distal raphe endings terminating onto small helictoglossae ( Fig. 17 View FIGURE 1–17 )

Distribution and ecology: Mayamaea spirans is, to date, the only species in its genus recorded from marine habitats (see Barragan et al. 2017 and references therein). Although ecological details are sparse, it has been observed growing on other algae. Specimens from Sardinia, reported by Lange-Bertalot et al. (2003, pl. 16, fig. 6) in Pozza Dorgali, bear some resemblance to Hustedt’s taxon. Despite exhibiting less parallel valves, these specimens are the only ones with similarly short distal raphe ends. They were identified as “ Mayamaea (? nov.) spec. cf. spirans (Hustedt) Lange-Bertalot ,” confirming the occurrence of this taxon in diatom assemblages from ephemeral water bodies that nearly dry out during extended summer periods with limited precipitation, and that are predominantly associated with terrestrial diatom species. Mayamaea recondita ( Hustedt 1942: 68) Lange-Bertalot(1997:72) and Mayamaea arida ( Bock 1963: 223) Lange-Bertalot (1997: 72) also have short distal raphe ends. Nevertheless, they differ significantly in striae composition, with M. recondita exhibiting biseriate striae (see Barragán et al. 2017) and M. arida featuring a single elongated oval areola ( Bagmet et al. 2021).