Rhoicosphenula Lange-Bert., Kociolek, A.A.Saber & Cantonati, 2021

Saber, Abdullah A., Angeli, Nicola, Lange-Bertalot, Horst, Kociolek, John P., Spitale, Daniel, Charles, Donald F. & Cantonati, Marco, 2021, Rise of subgen. Rhoicosphenula Lange-Bert. to the genus level, and description of a new Gomphosphenia s. s. species from Puerto Rico, Cryptogamie, Algologie 20 (13), pp. 217-229 : 221

Rhoicosphenula Lange-Bert., Kociolek, A.A.Saber & Cantonati , stat. nov.

( Figs 2 , 3 )

Rhoicosphenula Lange-Bert. Nova Hedwigia 60: 244 (1995).

Cells solitary, not forming colonies or aggregates, growing as epiphytes on small mucilaginous stalks. Frustules almost rectangular in girdle view, sometimes appearing slightly broadly wedge-shaped ( Fig. 2 G-I). Pseudosepta present on both poles of the valves. Raphe branches straight, with large, well-separated proximal ends ( Fig. 2 A-F), and with T-shaped distal fissures ( Fig. 3A ). Internal fissures extend onto the central nodule, with short and very faintly bent proximal ends ( Fig. 3C, H ). Foramina of the areolae simple, more or less slit-shaped, forming two systems, one on the valve face and one on the mantle, respectively, separated by a hyaline mantle margin ( Fig. 3A, B ). Areolae are covered internally by flat hymenes (similar to those of Brachysira ), developing from the sternum to the mantle without any visible interruption ( Fig. 3F, G ). The cingulum composed of six unilaterally open bands ( Fig. 3B ), including the valvocopula and first copula (each with a septum at one of the poles), as well as the four further copulae ( Fig. 3C, D ).

REGISTRATION. — http://phycobank.org/102718

New combinations within Rhoicosphenula stat. nov.:

Figures

FIG. 2. — LM micrographs of the generitype species (R. paradoxa) of Rhoicosphenula Lange-Bert.,Kociolek, A.A.Saber & Cantonati,stat. nov.,depicting the valve size-diminution series in valve (A-F) and girdle view (G-I); G undergoing division process) of the holotype specimens. Note the pseudosepta at the head- and footpole, the proximal raphe pores which are well separated and broadened (A-F) whilst the internal endings are closer to each other (see e.g., bright contours in B). Scale bar: 10 μm. From Lange-Bertalot (1995) mod.

FIG. 3. — SEM micrographs of the generitype species (R. paradoxa) of Rhoicosphenula Lange-Bert., Kociolek, A.A.Saber & Cantonati, stat. nov. External views (A, B); internal views (C-H): A, complete frustule (note the slit-like areole on valve face and mantle); B, hypovalve (left) with footpole immersed in the six girdle bands, which appear totally hyaline; they are alternately open and closed at each pole; C, valve with apposed valvocopula and a further copula; D, headpole; the valvocopula forms a septum; the valve pseudoseptum is thus mostly covered, only a triangle remains visible; E, valve footpole with pseudoseptum and open valvocopula (no further copula); F, exposed fracture of the right valve margin: the transapical ribs and the alveoli covered by hymenes become visible; G, exposed fracture at the pseudoseptum; H, the corroded hymenes allow a view of the areolae which are more numerous and differently shaped than the slit-like external foramina. Scale bars: A, C, 2 μm; B, D-H, 1 μm. From Lange-Bertalot (1995) mod.