Diatomella balfouriana Greville (1855: 259)

Furey, Paula C., Manoylov, Kalina M. & Lowe, Rex L., 2020, New and interesting aerial diatom assemblages from southwestern Iceland, Phytotaxa 428 (3), pp. 173-208 : 195-196

Diatomella balfouriana Greville (1855: 259) (LM = Fig. 10 A–E)

Valves in our material show biseriate striae on the deep mantles and volvocapulae with evidence of septa, each with an opening at each apex and in the central area. Though previously reported from Iceland ( Hallgrímsson 2007, Foged 1974), this taxon, typically not common in our samples, occurred at 28% relative abundance at one site (WW 42) in the Þingvellir rift valley ( Table 2).

Hygropetra balfouriana (Grunow ex Cleve 1895: 80) Krammer et Lange-Bertalot in Krammer (2000: 206) (LM = Fig. 2 Q–R; SEM = Fig. 2 U–V)

Valves with ghost filiform raphe ( Fig. 2 R), girdle view shows rounded ends ( Fig. 2 R). Valve face curved at the margins into a narrow valve mantle. Striae broad, radiate throughout, structured by several rows of areolae, narrowing into a “V” shape towards the axial area and rounded on the mantle ( Fig. 2 U). Valve morphology measured at length 5.1–9.6 μm, width middle 2.8–4.1 μm, and striae 9–10 striae in 10 μm (for n=16 LM, n=7 SEM). Some areolae closed by vela. Visible transapical costae in the valve internal view and distant proximal raphe endings ( Fig. 2 V). Septa in girdle bands not evident, but irregular linear slits on the volvocopula volvocapula ( Fig. 2 U). The algal taxa lists from Iceland, Hallgrímsson (2007) and Foged (1974), include this species as Pinnularia balfouriana Grunow ex Cleve (1895: 80) . Not common at sites, but in Hengill, H. balfouriana specimens occurred at>5 – 10% relative abundance at one site,>10%–20% at another, and at 59.6% at WW 53 ( Table 2).

Melosira varians Agardh (1827: 628)

Valves occurred infrequently in general, but were present at 15% relative abundance at a site along the highland road, Landmannaleið, before Fjallabak and at <1% further along Landmannaleið.

Orthoseira roeseana ( Rabenhorst 1848 –1860: 383) Pfitzer (1871: 134) (LM = Fig. 2 N, S, T; SEM = Fig. 3)

Valves of Orthoseira roeseana from rock scrapings in Iceland had a disc shaped valve face, 13–34.1 µm in diameter, which formed a right angle to the valve mantle, 8–15 µm long. The mantle contained uniseriate striae, 13–15 in 10 µm ( Figs 2 N, 3 D). Areolae on the valve face occurred as small, round, uniseriate striae covering 4/5 th of the valve face ( Figs 2 S, T, 3 A–D). The middle hyaline area contained 3 to 4 carinoportulae with a rim, a feature typical of this genus ( Round et al. 1990, Crawford 1981, Houk 1993). Short chains were observed. Valves were present with and without spines. When present, marginal spines were straight and spatulate in form, and arranged with distinct pores between them ( Fig. 2 T, 3 D). Perforations were present on the girdle bands ( Fig. 3 D).

Specimens from Iceland fit into the Orthoseira roeseana complex due to the presence of carinoportulae, linking spines, and a fairly deep mantle ( Round et al. 1990). The radiate striae and number of carinoportulae distinguish Orthoseira roeseana from O. johansenii Lowe et Kociolek in Lowe et al. (2013: 46) ( Lowe et al. 2013).The absence of rimoportulae (slits) between carinoportulae contrasts with Orthoseira species where this feature occurs such as O. verleyenii Van de Vijver in Lowe et al. (2013: 41) from lava tubes in Île Amsterdam ( Lowe et al. 2013), O. gremmenii Van de Vijver et Kopalová (2008: 108) from the small volcanic Gough Island, southern Atlantic Ocean ( Van de Vijver & Kopalová, 2008), O. limnopolarensis Van de Vijver et Crawford (2014: 248) from a sediment core Livingston Island (South Shetland Islands, Antarctica) ( Van de Vijver & Crawford 2014), and Orthoseira taxon 1 and 2 from Madagascar ( Spaulding & Kociolek 1998).

Valves occurred infrequently in general, but relative abundance occurred at 12% (WW 20) in Hengill and at 2.6% (WW 51) along Landmannaleið. Both sites contained some moss, a typical association for this genus ( Roldán & Hernández-Mariné 2009). This taxon is also commonly reported from moist soils, wet walls, waterfall spray zones, and wet but not submerged habitats ( Lowe et al. 2013).

Platessa rupestris var. interrupta ( Krasske 1932: 105) Lange-Bertalot in Krammer & Lange-Bertalot (2004: 445) (LM = Figs 10 M–O, a; 12 B)

Valves similar in size to P. rupestris , but the striae constantly interrupted outlining the central area in both valves in our site, therefore we kept this taxon separate. Observed at>5% relative abundance in one site (WW 54).

Psammothidium marginulatum (Grunow in Cleve & Grunow 1880: 21) Bukhtiyarova et Round (1996: 3) (LM = Fig. 10 Y–Z)

The rapheless valve has marginal striae and adjacent to them a series of ornamentations, on the raphe valve outline irregular axial area, central area wide, rectangular, surrounded by 8 short striae ( Fig. 10 Y, Z). Observed at 18.7% relative abundance in one site (WW 55) in Hengill ( Table 2) and in low abundance at WW 3, 52, and 54.

Stauroneis cf. borrichii (J.B. Petersen 1915: 285) J.W.G. Lund (1946: 63) (LM = Fig. 11 X– a)

Valves, linear/lanceolate with parallel sides and broadly rounded ends, measured at length 23–38 µm, width 5.5–7 µm, and 25–28 striae in 10 µm (for n=10 LM). We used cf. as the length reported in the literature does not go above 30 µm. Axial area linear, narrow. Central area a rectangular fascia with isolated irregularly short striae, widening towards the margins. Raphe filiform, straight with indistinct central pores. Terminal fissures clearly visible, deflected. Transapical striae radiate in the middle, parallel to convergent near the poles. Absent from most wet walls, but present at>5% but <10% relative abundance at one site in Hengill and another in Þingvellir rift valley. Reported as able to survive desiccation ( Petersen 1928a).

Staurosirella neopinnata Morales, Wetzel, Haworth et Ector (2019: 82) (LM = Fig. 2 B–G; SEM = Fig. 2 A)

In girdle view, frustules are rectangular and form ribbon-like colonies, joined by linking spines ( Fig. 2 A), girdle consists of 5 separate copulae, slightly curved near the poles. Valves linear to elliptical lanceolate, no heteropolarity was observed length 10–25 µm, width 3–4.5 µm, 10 striae in 10µ, (for n=10 LM, n=5 SEM). Axial area fairly narrow, linear to slightly lanceolate. Striae parallel, composed of slit-like areolae, continuing without interruption onto the mantle ( Fig. 2 A). Marginal spines almost always detected. No rimoportula, but one or two apical pore fields present. Generally rare or in low abundance at our sites, with the exception of one site (WW 3) where the relative abundance was 20% ( Table 2).