Staurophora brantii Bahls, 2012

Bahls, Loren, 2012, Staurophora brantii, a new diatom (Bacillariophyta, Anomoeoneidaceae) from the northwestern Great Plains, USA, Phytotaxa 39, pp. 31-37 : 32-35

Staurophora brantii Bahls , sp. nov. ( Figs 1–10, 18–27)

Cellulae solitariae. Unus lobus chloroplastus locatus juxta cingulum. Valvae ellipticae-lanceolatae usque rhombicaelanceolatae, apices latus rotundi usque leviter rostrati; superficies valvarum leviter curvus vel pallium. Longitudo valvae 38–48 µm, latitudo valvae 9–12 µm. Rhaphis directa, filiformis; extremas proximales rhaphis inflatus et leviter curvae; extremas distales rhaphis fortiter curvae. Area axiale angusta linearae, leviter latus prope area centralis; area centralis latus fascia, interdum nonnullus marginum striae brevis. Striae radiantes et subtiliter punctata, (14) 18–24 in 10 µm.

Type:— USA. Montana: Crow Creek above East Powderville Road Bridge , Powder River County, 45 o 40’ 44” N, 105 o 07’ 19” W. Sample collected from surface sediment by Montana DEQ personnel on 1 st August 2007 . Montana Diatom Collection sample number 411202 ( holotype slide ANSP GC64897 , circled specimen on slide [= Fig. 3], isotypes: circled specimens on slides ANSP GC64898 , MDC 32–60 and MDC 116–59) .

Cells solitary, lying mostly in valve view, within a laminated mucilage capsule ( Fig. 1). One lobed plastid with a large lenticular pyrenoid positioned against the girdle opposite the nucleus ( Figs. 1, 2). Valves ellipticlanceolate to rhombic-lanceolate, apices broadly rounded and somewhat protracted ( Figs 5–10). Valve face curved in transapical section, merging gradually into the mantle ( Figs 19, 20), mantle shallower near the ends ( Fig. 20). Valve length 38–48 µm; valve width 9–12 µm. Raphe sternum narrow, somewhat thickened and slightly elevated at the central nodule ( Fig. 20). Overlapping girdle elements bear longitudinal rows of small round poroids ( Fig. 23). Raphe straight, filiform. External proximal raphe endings bordered by lips and lying in spathulate grooves ( Figs 24, 25); terminal fissures strongly curved, opening toward the secondary side of the valve ( Fig. 22). Internal proximal raphe endings bent in the same direction ( Fig. 27); terminal fissures end in helictoglossae ( Fig. 26). Axial area narrow, linear, widening slightly near the central area. Central area a transverse fascia, wider toward the margins and with a few shortened striae on one or both sides. Only the ends of the longest of these short striae are visible in valve view, making them appear to be more widely spaced than other striae ( Fig. 20). Striae radiate and uniseriate, 18–24 in 10 µm ( 14 in 10 µm, initial valve, Fig. 10), but more concentrated toward the poles. Striae composed of small round areolae.

Etymology:— This taxon is named in honour of Dr. Lynn A. Brant of Cedar Falls, Iowa, USA.

Observations:— Staurophora brantii can be compared to similar species that have a transverse fascia and a preference for waters with elevated electrolytes: Staurophora amphioxys (W.Greg.) D.G.Mann , Staurophora caljonii Cocquyt , Staurophora elata (Hust.) D.G.Mann , Staurophora salina (W.Sm.) Mereschk. , and Staurophora wislouchii (Poretzky & Anisimova) D.G.Mann ; Stauroneis atacamae Hust. , Stauroneis dubitabilis Hust. , Stauroneis submarina Hust. and Stauroneis tackei (Hust.) Krammer & Lange-Bert. Several of these were originally placed in the genus Stauroneis , although currently Stauroneis sensu stricto is limited to species occurring in freshwater habitats only ( Round et al. 1990).Other brackish to marine taxa considered for comparison were dismissed because they have radically different valve outlines, e.g., Stauroneis desiderata Cleve , Stauroneis pachycephala Cleve , and Stauroneis rossii Hendey.

Staurophora brantii may be distinguished from most of those listed above by its size, valve and end shape, striae count, and habitat. Although similar in most of these features, Stauroneis submarina Hust. has a narrow linear central area, unlike the broad deltoid central area of Staurophora brantii .

Staurophora brantii overlaps in distribution and shares some habitats on the Northwestern Great Plains with two closely allied taxa: Stauroneis tackei is much smaller and has linear-lanceolate valves ( Figs 11–14), while Staurophora wislouchii has broadly elliptical valves with short protracted ends ( Figs 15–17).

Habitat, Ecology and Distribution:— Staurophora brantii lives on fine sediments in streams of the Northwestern Great Plains. Most streams in this ecoregion are ephemeral or intermittent, typically consisting of a series of interconnected pools with bottoms composed of fine silt and decomposing organic matter. Records of this taxon in the Montana Diatom Database are distributed by state as follows: Montana (118), North Dakota (3), South Dakota (10), and Wyoming (20). Abundance-weighted mean values for water quality variables in streams where Staurophora brantii occurs suggest that it prefers fresh alkaline waters with somewhat elevated concentrations of electrolytes, particularly sodium and sulfate. The most frequently cooccurring associates of Staurophora brantii are largely mobile, epipelic taxa that prefer elevated concentrations of dissolved solids.