Stigmagloia lobbanii Glushchenko, Kezlya, Kapustin & Kulikovskiy 2024, sp. nov.

Stigmagloia lobbanii Glushchenko, Kezlya, Kapustin & Kulikovskiy, sp. nov. (Figs 1–43) LM description (Figs 1–21):— Valves elliptical with rostrate ends. Length 28.0–29.3 µm, width 13.7–14.6 µm. Axial area narrow, linear. Central area asymmetrical, small, longitudinally elongated. Raphe fine, weakly lateral. In the central part of the valve, at some distance from the central area, there is one isolated stigma (Fig. 4, black arrow). Transapical striae at the central part of the valve are parallel, becoming weakly radiate towards the apices, 23–24 in 10 µm. Pseudoloculi clearly visible in LM. Girdle bands are open (Figs 20, 21). Partecta are square or rectangular, of the same size, 1 µm wide, 11 in 10 µm. The partecta of the partectal ring are distributed evenly, and almost reach the apices of the valve (Figs 17–21). SEM, external view (Figs 22–29):— The raphe branches strongly sinuous, lateral, reverse lateral about midway from the apices to the central area (Figs 22, 23). Central raphe ends slightly raised above the valve surface, extended and curved in the same direction (Fig. 24, black arrows). In the central raphe slits are visible the internal raphe slits (Fig. 25, black arrows). Distal raphe ends unilaterally deflected (in the opposite direction from the central raphe ends) to the valve margin (Fig. 22, black arrowheads). Striae are separated by slightly raised longitudinal ribs (Figs 23, 24, 28, white arrows). Pseudoloculi openings are located at a slight angle relative to the valve surface (Figs 22–29). Transapical pseudoloculi have a rounded or transversely elongated shape (Figs 24, 25, 28, black arrowheads), 14–16 in 10 µm. On the border valve mantle/face junction a small marginal hyaline ridge is present (Figs 22, 28, black arrows). There is one row of pseudoloculi on the valve margin (Figs 22, 28, white arrowheads). The stigma is a round cratershaped depression with a diameter of 0.6 µm (Figs 26, 27, black arrows), in which there are 5–6 outgrowths located radially (Figs 26, 27, white arrows). The valve apices do not have pseudoloculi (Figs 29, black arrowhead). SEM, internal view (Figs 30–43):— Valve face is flat (Figs 30, 31). Raphe branches almost straight (Fig. 30, black arrows). Central raphe ends are simple, straight (Figs 30, 37, white arrows). Distal raphe ends terminate in small helictoglossae, located near the valve apices (Figs 31, 41, 43, black arrows). Pseudoloculi form noticeable longitudinal rows, sometimes undulating, one of the rows closest to the axial area is almost straight, and the opposite one is clearly curved (Figs 31, 36, white arrows). Pseudoloculi rounded and elongated, covered by vola (Figs 37, 38, black arrows). Areolae one to four per pseudoloculum (Fig. 34, black arrowheads). The valve mantle is low, has one row of large elongated pseudoloculi (Figs 31, 42, 43, white arrowheads). The stigma also lies in a round depression, but of lesser depth than on the outer surface (Figs 39, 40, black arrows). The growths in the stigma are also clearly visible (Figs 39, 40, white arrows). At each valves end there is a distinct pseudosepta (Fig. 30, black arrowhead). The valvocopula has a partectal ring (Figs 32, 34, 35, black arrows). In the destroyed partectal chambers, the remains of partitions are clearly visible (Fig. 33, black arrow). The partectal chambers have rows of thin simple perforations (Figs 33, 34, white arrow). Closer to the apices, the copula noticeably narrows, there are no chambers (Fig. 35, white arrows). Type:— Viet Nam, South China Sea, Khánh Hòa Province, Nha Trang, epilithon (N 12°12’27.280”, E109°12’56.021”); leg. M.S. Kulikovskiy in April 2018. Slide no. 09255 from oxidized culture strain no. SVN638, isolated from sample NTs 65 deposited in herbarium of MHA, Main Botanical Garden, Russian Academy of Science, Moscow, Russia. Holotype specimen illustrated in Figure 3. Isotype: Slide no. 09255a deposited in collection of Maxim Kulikovskiy at the Herbarium of the Institute of Plant Physiology Russian Academy of Sciences, Moscow, Russia. Reference strain:— SVN638, isolated from the sample NTs 65, deposited in the culture collection of the Laboratory of Molecular Systematics of Aquatic Plants, K.A. Timiryazev Institute of Plant Physiology, Russian Academy of Sciences (Moscow, Russia). Sequence data: —Partial SSU rDNA gene sequence comprising V 4 domain sequence (GenBank accession number PQ571200) and partial rbc L sequence (GenBank accession number PQ589835) for the strain SVN638. Etymology: —The species is named after Dr. Christopher S. Lobban (b. 1950), a Professor Emeritus at the University of Guam, for his significant contribution to the study of marine diatoms. Distribution:— As yet known only from the type locality.