Divergita capillaris (Grunow) Theriot, 2018

Sabir, J. S. M., Theriot, E. C., Lobban, C. S., Alhebshi, A. M., Al-Malki, A. L., Hajrah, N. H., Khiyami, M. A., Obaid, A. Y., Jansen, R. K. & Ashworth, M. A., 2018, Systematics of araphid diatoms with asymmetric rimoportulae or densely packed virgae, with particular attention to Hyalosynedra (Ulnariaceae, Bacillariophyta), Phytotaxa 347 (1), pp. 1-49 : 25

Divergita capillaris (Grunow) Theriot comb. nov. ( Figs 54—61 )

Basionym: — Synedra capillaris Grunow (1877 , 168)

Lectotype: —Naturhistorisches Museum Wein, Grunow 839.

Material studied: —Grunow 839 and 840, Naturhistorisches Museum Wein.

Description: —Grunow described S. capillaris from Honduras material as being 225 μm long and 1.5–2 μm wide with 19 striae in 10 μm long, and emphasized that the valve was very narrow. His one illustration (Pl. CXCIV, Fig. 2 ) showed a diatom of these dimensions that was weakly curved along the apical axis, and whose apices were not distinctly expanded. We found a few long, curved, narrow synedroid diatoms on the Grunow 839 mica with coarser virga densities than that of H. laevigata ( Fig 54 ). Other similar specimens, mounted in Naphrax, were straight to weakly curved along the apical axis, and measured 135.5–297.0 μm long by 2.9–4.2 μm wide ( Figs 55, 56 , 59 ). The valve ends were expanded, indistinctly on some specimens, but distinctly so on others. A rimoportula occurred at each pole, and each was weakly asymmetric ( Fig 60 ). The external pore pattern was again decussate ( Fig 61 ). Virgae numbered 18–20 in 10 μm along the transapical axis at the sternum ( Fig 61 ). The internal membrane was perforated at the face-mantle junction by a single pore between each pair of virgae. The apical pore fields gave the barest suggestion of being sunken (arguably were not sunken at all) and lacked spines.

Remarks: —All Grunow (1877) had to say of the geography of S. capillaris was “Rare in the Honduras gathering.” Finding it in greatest abundance on the Grunow 839 mica, we selected that as the lectotype. We effected the transfer of S. capillaris to Divergita because specimens from Grunow 839 were observed to have the characteristic ultrastructural features of other Divergita species, an asymmetric rimoportula at each pole, a very shallow ocellulimbus which was wide (16+ pores wide) and short (3 pores tall), and especially the decussate areolar pattern. This species differed slightly in outline from the other large species, D. toxoneides , in that the valve margins are less attenuated, giving the appearance of a broader valve end region in D. capillaris . At the same time, D. capillaris was much narrower than the WK 57 specimen, and wild specimens of D. toxoneides reported by Perez-Coca et al. (2017).

Figures

FIGURES 54–58. Divergita capillaris from Grunow 839. 54. LM of whole strongly curved valve from mica. 55. LM of whole strongly curved valve from Naphrax preparation. 56. SEM of broken weakly curved valve (interior view). 57. SEM detail of interior of apex of valve of 56. 58. SEM detail of central area, internal view, of valve of 56.

FIGURES 59–61. Divergita capillaris from Grunow 839. 59. Interior view of broken strongly curved valve. 60. Detail of interior apex from same valve as 59. Note obvious expansion of terminus into a capitate or subcaptitate morphology. 61. Exterior detail of apex showing barely perceptibly sunken pore field and decussating areolar pattern. This specimen had a weakly expanded apex.

FIGURES 2–4. Hyalosynedra laevigata from Grunow 839. 2. Bright field LM of large specimen. 3. Differential interference contrast LM of large specimen. 4. External view of entire valve in SEM.