Rhoicosphenia johannessoniae Al-Handal, Levkov & Wulff sp. nov. (Figs 1–11, 12–25)

Description

LM observation (Figs 1–11): Valves heteropolar, narrowly clavate, 29–48 μm long and 6.8–8.5 μm wide. Head pole narrowly rounded, base pole protracted to elongated subcapitate with rounded apex. Raphe filiform on the R-valve with distinct proximal endings (Figs 1–5), but not resolvable on the D-valve (Figs 6–10). Axial area linear and very narrow on R-valve with indistinct central area. D-valve axial area narrowly linear lanceolate. Striae on both valves parallel to slightly radiate, 20–22 in 10 μm. Areolae not discernible in LM. Frustules in girdle view bent and wedge shaped (Fig. 11).

SEM observations (Figs 12–25): R-valves: Valves concave and narrowly clavate with broadly rounded poles (Figs 12, 13). Externally, head poles broadly rounded (Figs 16, 18), base pole narrowly rounded and protracted, with pore field of irregularly arranged poroids, formed of 11–12 rows.Axial area linear and asymmetric, becoming narrower near poles (Fig. 12). Central area slightly wider than axial area, and in some specimens, ornamented with small porelike depressions that do not penetrate internally (Figs 12, 17). Central area not located in valve centre but positioned below the wider middle part of the valve towards the base pole (Fig. 12). Raphe filiform, proximal endings small, droplike and distantly spaced (Fig. 17). Distal raphe endings curved and terminate on valve mantle (Fig. 16). Striae parallel to slightly radiate and formed of slit-like, weakly curved areolae (Figs 13, 16). Internally, pseudosepta on both poles large and strongly silicified (Fig. 14). Axial area lanceolate, gradually widens into a large central area. Raphe proximal endings strongly hooked (Fig.15). Striae weakly radiate in valve centre and separated by well-developed virgae (Fig. 15). D-Valves: Valves concave, narrowly clavate with rounded poles (Figs 19–21). Base pole protracted with 10–12 irregularly arranged rows of poroids which form pore field (Figs 20, 21, 23). Axial area linear, very narrow, slightly widened towards mid- valve (Fig. 20). Raphe system reduced, the upper raphe fissure very short, slightly bent, extends for 4–5 striae and positioned near the head pole (Fig. 24). Raphe fissure at base pole straight, longer than upper fissure with weakly curved distal endings that reach valve margin (Fig. 23). Striae parallel, formed of slit-like areolae, occasionally biseriate stria formed near valve margin (Figs 21, 22). Internally, head pole rounded (Fig. 19), while base pole rostrate (Fig. 25). Axial area linear-lanceolate. Proximal raphe endings crook-shaped (Fig. 25). Striae parallel, narrow in mid- valve and wider toward poles (Fig. 19). Pseudosepta of base pole interrupted by lacuna which terminate before valve apex with rounded and slightly bent structure (Fig. 25).

Type: Grisslehamn port, Baltic coast of Sweden, 60° 05’ 53’’ N, 18° 48’ 47’’ E, Collectors: Adil Al-Handal and Mikael Hedblom, collection date: May 2019. Permanent slide containing cells of R. johannessoniae is deposited at the Macedonian National Diatom collection under accession No. MKNDC 014457. Figures 2 and 7 represent the holotype .

Isotype: Permanent slide containing cells of R. johannessoniae is deposited at the University of Gothenburg Herbarium under No. GB-0210437.

Etymology: The epithet is in honour of Professor Kerstin Johannesson of the Tjärnö Marine Laboratory, University of Gothenburg for her contribution and outstanding work on the ecology and phylogeny of some marine benthic invertebrate in Sweden.

Ecology: Rhoicosphenia johannessoniae was rather rare and constituted 0.8% of the diatom association in the sample examined. It is a brackish water species found epiphytic on the brown macrophyte Ectocarpus siliculosus and did not appear on other macrophytes collected from the same region or in the benthic samples. Water temperature was 12.3 °C and salinity 4.9 psu. Several other species were associated with R. johannessoniae including Licmophora gracilis (Ehrenberg) Grunow (1867:34, 24.6%), Licmophora ehrenbergii (Kützing) Grunow (1867: 36, 10.2%), Entomoneis paludosa (W.Smith) Reimer 1975: 4, 5.3%), Diatoma tenuis C. Agardh (1812: 15, 3.4%), Tabularia fasciculata (C.Agardh) Williams & Round (1986:326, 2.7%), together with small-sized Navicula spp. and Nitzschia spp.